ParallelEnumerable.cs :  » 2.6.4-mono-.net-core » System.Linq » System » Linq » C# / CSharp Open Source

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C# / CSharp Open Source » 2.6.4 mono .net core » System.Linq 
System.Linq » System » Linq » ParallelEnumerable.cs
#if NET_4_0
//
// ParallelEnumerable.cs
//
// Author:
//       Jrmie "Garuma" Laval <jeremie.laval@gmail.com>
//
// Copyright (c) 2010 Jrmie "Garuma" Laval
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.

using System;
using System.Threading;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Concurrent;

namespace System.Linq{
  public static class ParallelEnumerable
  {
    #region Range & Repeat
    public static ParallelQuery<int> Range (int start, int count)
    {
      if (int.MaxValue - start < count)
        throw new ArgumentOutOfRangeException ("count", "start + count - 1 is larger than Int32.MaxValue");
      if (count < 0)
        throw new ArgumentOutOfRangeException ("count", "count is less than 0");

      return (new RangeList (start, count)).AsParallel ();
    }

    public static ParallelQuery<TResult> Repeat<TResult> (TResult obj, int count)
    {
      if (count < 0)
        throw new ArgumentOutOfRangeException ("count", "count is less than 0");

      return (new RepeatList<TResult> (obj, count)).AsParallel ();
    }
    #endregion

    #region Empty
    public static ParallelQuery<TResult> Empty<TResult> ()
    {
      return Repeat<TResult> (default (TResult), 0);
    }
    #endregion

    #region AsParallel
    public static ParallelQuery<TSource> AsParallel<TSource> (this IEnumerable<TSource> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return new ParallelQuery<TSource> (new QueryStartNode<TSource> (source));
    }

    public static ParallelQuery<TSource> AsParallel<TSource> (this Partitioner<TSource> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return new ParallelQuery<TSource> (new QueryStartNode<TSource> (source));
    }

    public static ParallelQuery AsParallel (this IEnumerable source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return new ParallelQuery<object> (new QueryStartNode<object> (source.Cast<object> ()));
    }

    public static IEnumerable<TSource> AsEnumerable<TSource> (this ParallelQuery<TSource> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.AsSequential ();
    }

    public static IEnumerable<TSource> AsSequential<TSource> (  this ParallelQuery<TSource> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Node.GetSequential ();
    }
    #endregion

    #region AsOrdered / AsUnordered
    public static ParallelQuery<TSource> AsOrdered<TSource> (this ParallelQuery<TSource> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return new ParallelQuery<TSource> (new QueryAsOrderedNode<TSource> (source.Node));
    }

    public static ParallelQuery<TSource> AsUnordered<TSource> (this ParallelQuery<TSource> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return new ParallelQuery<TSource> (new QueryAsUnorderedNode<TSource> (source.Node));
    }

    public static ParallelQuery AsOrdered (this ParallelQuery source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.TypedQuery.AsOrdered ();
    }
    #endregion

    #region With*
    public static ParallelQuery<TSource> WithExecutionMode<TSource> (this ParallelQuery<TSource> source,
                                                                     ParallelExecutionMode executionMode)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return new ParallelQuery<TSource> (new ParallelExecutionModeNode<TSource> (executionMode, source.Node));
    }

    public static ParallelQuery<TSource> WithCancellation<TSource> (this ParallelQuery<TSource> source,
                                                                    CancellationToken cancellationToken)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return new ParallelQuery<TSource> (new CancellationTokenNode<TSource> (cancellationToken, source.Node));
    }

    public static ParallelQuery<TSource> WithMergeOptions<TSource> (this ParallelQuery<TSource> source,
                                                                    ParallelMergeOptions mergeOptions)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return new ParallelQuery<TSource> (new ParallelMergeOptionsNode<TSource> (mergeOptions, source.Node));
    }

    public static ParallelQuery<TSource> WithDegreeOfParallelism<TSource> (this ParallelQuery<TSource> source,
                                                                           int degreeParallelism)
    {
      if (degreeParallelism < 1 || degreeParallelism > 63)
        throw new ArgumentException ("degreeOfParallelism is less than 1 or greater than 63", "degreeParallelism");
      if (source == null)
        throw new ArgumentNullException ("source");

      return new ParallelQuery<TSource> (new DegreeOfParallelismNode<TSource> (degreeParallelism, source.Node));
    }

    internal static ParallelQuery<TSource> WithImplementerToken<TSource> (this ParallelQuery<TSource> source,
                                                                          CancellationTokenSource token)
    {
      return new ParallelQuery<TSource> (new ImplementerTokenNode<TSource> (token, source.Node));
    }
    #endregion

    #region Select
    public static ParallelQuery<TResult> Select<TSource, TResult> (this ParallelQuery<TSource> source, Func<TSource, TResult> selector)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (selector == null)
        throw new ArgumentNullException ("selector");

      return new ParallelQuery<TResult> (new QuerySelectNode<TResult, TSource> (source.Node, selector));
    }

    public static ParallelQuery<TResult> Select<TSource, TResult> (this ParallelQuery<TSource> source, Func<TSource, int, TResult> selector)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (selector == null)
        throw new ArgumentNullException ("selector");

      return new ParallelQuery<TResult> (new QuerySelectNode<TResult, TSource> (source.Node, selector));
    }
    #endregion
    
    #region SelectMany
    public static ParallelQuery<TResult> SelectMany<TSource, TResult> (this ParallelQuery<TSource> source,
                                                                       Func<TSource, IEnumerable<TResult>> selector)
    {
      return source.SelectMany (selector, (s, e) => e);
    }

    public static ParallelQuery<TResult> SelectMany<TSource, TResult> (this ParallelQuery<TSource> source,
                                                                       Func<TSource, int, IEnumerable<TResult>> selector)
    {
      return source.SelectMany (selector, (s, e) => e);
    }
    
    public static ParallelQuery<TResult> SelectMany<TSource, TCollection, TResult> (this ParallelQuery<TSource> source,
                                                                                    Func<TSource, IEnumerable<TCollection>> collectionSelector,
                                                                                    Func<TSource, TCollection, TResult> resultSelector)
    {
      return new ParallelQuery<TResult> (new QuerySelectManyNode<TSource, TCollection, TResult> (source.Node,
                                                                                                 collectionSelector,
                                                                                                 resultSelector));
    }
    
    public static ParallelQuery<TResult> SelectMany<TSource, TCollection, TResult> (this ParallelQuery<TSource> source,
                                                                                    Func<TSource, int, IEnumerable<TCollection>> collectionSelector,
                                                                                    Func<TSource, TCollection, TResult> resultSelector)
    {
      return new ParallelQuery<TResult> (new QuerySelectManyNode<TSource, TCollection, TResult> (source.Node,
                                                                                                 collectionSelector,
                                                                                                 resultSelector));
    }
    #endregion

    #region Where
    public static ParallelQuery<TSource> Where<TSource> (this ParallelQuery<TSource> source, Func<TSource, bool> predicate)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (predicate == null)
        throw new ArgumentNullException ("predicate");

      return new ParallelQuery<TSource> (new QueryWhereNode<TSource> (source.Node, predicate));
    }

    public static ParallelQuery<TSource> Where<TSource> (this ParallelQuery<TSource> source, Func<TSource, int, bool> predicate)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (predicate == null)
        throw new ArgumentNullException ("predicate");

      return new ParallelQuery<TSource> (new QueryWhereNode<TSource> (source.Node, predicate));
    }
    #endregion

    #region Aggregate
    public static TSource Aggregate<TSource> (this ParallelQuery<TSource> source, Func<TSource, TSource, TSource> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Aggregate<TSource, TSource, TSource> ((Func<TSource>)null,
                                                          func,
                                                          func,
                                                          (e) => e);
    }

    public static TAccumulate Aggregate<TSource, TAccumulate> (this ParallelQuery<TSource> source,
                                                                 TAccumulate seed,
                                                                 Func<TAccumulate, TSource, TAccumulate> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Aggregate (seed, func, (e) => e);
    }

    public static TResult Aggregate<TSource, TAccumulate, TResult> (this ParallelQuery<TSource> source,
                                                                      TAccumulate seed,
                                                                      Func<TAccumulate, TSource, TAccumulate> func,
                                                                      Func<TAccumulate, TResult> resultSelector)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");
      if (resultSelector == null)
        throw new ArgumentNullException ("resultSelector");

      TAccumulate accumulator = seed;

      foreach (TSource value in source)
        accumulator = func (accumulator, value);

      return resultSelector (accumulator);
    }

    public static TResult Aggregate<TSource, TAccumulate, TResult> (this ParallelQuery<TSource> source,
                                                                      TAccumulate seed,
                                                                      Func<TAccumulate, TSource, TAccumulate> updateAccumulatorFunc,
                                                                      Func<TAccumulate, TAccumulate, TAccumulate> combineAccumulatorsFunc,
                                                                      Func<TAccumulate, TResult> resultSelector)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (updateAccumulatorFunc == null)
        throw new ArgumentNullException ("updateAccumulatorFunc");
      if (combineAccumulatorsFunc == null)
        throw new ArgumentNullException ("combineAccumulatorsFunc");
      if (resultSelector == null)
        throw new ArgumentNullException ("resultSelector");

      return source.Aggregate (() => seed, updateAccumulatorFunc, combineAccumulatorsFunc, resultSelector);
    }

    public static TResult Aggregate<TSource, TAccumulate, TResult> (this ParallelQuery<TSource> source,
                                                                      Func<TAccumulate> seedFunc,
                                                                      Func<TAccumulate, TSource, TAccumulate> updateAccumulatorFunc,
                                                                      Func<TAccumulate, TAccumulate, TAccumulate> combineAccumulatorsFunc,
                                                                      Func<TAccumulate, TResult> resultSelector)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (seedFunc == null)
        throw new ArgumentNullException ("seedFunc");
      if (updateAccumulatorFunc == null)
        throw new ArgumentNullException ("updateAccumulatorFunc");
      if (combineAccumulatorsFunc == null)
        throw new ArgumentNullException ("combineAccumulatorsFunc");
      if (resultSelector == null)
        throw new ArgumentNullException ("resultSelector");

      TAccumulate accumulator = default (TAccumulate);

      ParallelExecuter.ProcessAndAggregate<TSource, TAccumulate> (source.Node, seedFunc, updateAccumulatorFunc, (list) => {
        accumulator = list [0];
        for (int i = 1; i < list.Count; i++)
          accumulator = combineAccumulatorsFunc (accumulator, list[i]);
      });

      return resultSelector (accumulator);;
    }
    #endregion

    #region ForAll
    public static void ForAll<TSource> (this ParallelQuery<TSource> source, Action<TSource> action)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (action == null)
        throw new ArgumentNullException ("action");

      ParallelExecuter.ProcessAndBlock (source.Node, action);
    }
    #endregion

    #region OrderBy
    public static OrderedParallelQuery<TSource> OrderByDescending<TSource, TKey> (this ParallelQuery<TSource> source,
                                                                                  Func<TSource, TKey> keySelector,
                                                                                  IComparer<TKey> comparer)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (keySelector == null)
        throw new ArgumentNullException ("keySelector");
      if (comparer == null)
        throw new ArgumentNullException ("comparer");

      Comparison<TSource> comparison = (e1, e2) => -comparer.Compare (keySelector (e1), keySelector (e2));

      return new OrderedParallelQuery<TSource> (new QueryOrderByNode<TSource> (source.Node, comparison));
    }

    public static OrderedParallelQuery<TSource> OrderByDescending<TSource, TKey> (this ParallelQuery<TSource> source,
                                                                                  Func<TSource, TKey> keySelector)
    {
      return OrderByDescending (source, keySelector, Comparer<TKey>.Default);
    }

    public static OrderedParallelQuery<TSource> OrderBy<TSource, TKey> (this ParallelQuery<TSource> source,
                                                                        Func<TSource, TKey> keySelector)
    {
      return OrderBy (source, keySelector, Comparer<TKey>.Default);
    }

    public static OrderedParallelQuery<TSource> OrderBy<TSource, TKey> (this ParallelQuery<TSource> source,
                                                                        Func<TSource, TKey> keySelector,
                                                                        IComparer<TKey> comparer)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (keySelector == null)
        throw new ArgumentNullException ("keySelector");
      if (comparer == null)
        throw new ArgumentNullException ("comparer");

      Comparison<TSource> comparison = (e1, e2) => comparer.Compare (keySelector (e1), keySelector (e2));

      return new OrderedParallelQuery<TSource> (new QueryOrderByNode<TSource> (source.Node, comparison));
    }
    #endregion

    #region ThenBy
    public static OrderedParallelQuery<TSource> ThenBy<TSource, TKey> (this OrderedParallelQuery<TSource> source,
                                                                       Func<TSource, TKey> keySelector)
    {
      return ThenBy (source, keySelector, Comparer<TKey>.Default);
    }

    public static OrderedParallelQuery<TSource> ThenBy<TSource, TKey> (this OrderedParallelQuery<TSource> source,
                                                                       Func<TSource, TKey> keySelector,
                                                                       IComparer<TKey> comparer)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (keySelector == null)
        throw new ArgumentNullException ("keySelector");
      if (comparer == null)
        throw new ArgumentNullException ("comparer");

      Comparison<TSource> comparison = (e1, e2) => comparer.Compare (keySelector (e1), keySelector (e2));

      return new OrderedParallelQuery<TSource> (new QueryOrderByNode<TSource> (source.Node, comparison));
    }

    public static OrderedParallelQuery<TSource> ThenByDescending<TSource, TKey> (this OrderedParallelQuery<TSource> source,
                                                                                 Func<TSource, TKey> keySelector)
    {
      return ThenByDescending (source, keySelector, Comparer<TKey>.Default);
    }

    public static OrderedParallelQuery<TSource> ThenByDescending<TSource, TKey> (this OrderedParallelQuery<TSource> source,
                                                                                 Func<TSource, TKey> keySelector,
                                                                                 IComparer<TKey> comparer)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (keySelector == null)
        throw new ArgumentNullException ("keySelector");
      if (comparer == null)
        throw new ArgumentNullException ("comparer");

      Comparison<TSource> comparison = (e1, e2) => -comparer.Compare (keySelector (e1), keySelector (e2));

      return new OrderedParallelQuery<TSource> (new QueryOrderByNode<TSource> (source.Node, comparison));
    }
    #endregion

    #region All
    public static bool All<TSource> (this ParallelQuery<TSource> source, Func<TSource, bool> predicate)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (predicate == null)
        throw new ArgumentNullException ("predicate");

      CancellationTokenSource src = new CancellationTokenSource ();
      ParallelQuery<TSource> innerQuery = source.WithImplementerToken (src);

      bool result = true;
      innerQuery.ForAll ((e) => {
        if (!predicate (e)) {
          result = false;
          src.Cancel ();
        }
      });

      return result;
    }
    #endregion

    #region Any
    public static bool Any<TSource> (this ParallelQuery<TSource> source)
    {
      return Any<TSource> (source, (_) => true);
    }

    public static bool Any<TSource> (this ParallelQuery<TSource> source, Func<TSource, bool> predicate)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (predicate == null)
        throw new ArgumentNullException ("predicate");

      return !source.All ((e) => !predicate (e));
    }
    #endregion

    #region Contains
    public static bool Contains<TSource> (this ParallelQuery<TSource> source, TSource value)
    {
      return Contains<TSource> (source, value, EqualityComparer<TSource>.Default);
    }

    public static bool Contains<TSource> (this ParallelQuery<TSource> source, TSource value, IEqualityComparer<TSource> comparer)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (comparer == null)
        throw new ArgumentNullException ("comparer");

      return Any<TSource> (source, (e) => comparer.Equals (value));
    }
    #endregion

    #region SequenceEqual
    public static bool SequenceEqual<TSource> (this ParallelQuery<TSource> first,
                                               ParallelQuery<TSource> second)
    {
      if (first == null)
        throw new ArgumentNullException ("first");
      if (second == null)
        throw new ArgumentNullException ("second");

      return first.SequenceEqual (second, EqualityComparer<TSource>.Default);
    }

    public static bool SequenceEqual<TSource> (this ParallelQuery<TSource> first,
                                               ParallelQuery<TSource> second,
                                               IEqualityComparer<TSource> comparer)
    {
      if (first == null)
        throw new ArgumentNullException ("first");
      if (second == null)
        throw new ArgumentNullException ("second");
      if (comparer == null)
        throw new ArgumentNullException ("comparer");

      CancellationTokenSource source = new CancellationTokenSource ();
      ParallelQuery<bool> innerQuery
        = first.Zip (second, (e1, e2) => comparer.Equals (e1, e2)).Where ((e) => !e).WithImplementerToken (source);

      bool result = true;

      innerQuery.ForAll ((value) => {
        result = false;
        source.Cancel ();
      });

      return result;
    }

    [ObsoleteAttribute("The second data source of a binary operator must be of type System.Linq.ParallelQuery<T> rather "
                       + "than System.Collections.Generic.IEnumerable<T>. To fix this problem, use the AsParallel() "
                       + "extension method to convert the right data source to System.Linq.ParallelQuery<T>.")]
    public static bool SequenceEqual<TSource> (this ParallelQuery<TSource> first, IEnumerable<TSource> second)
    {
      throw new NotSupportedException ();
    }

    [ObsoleteAttribute("The second data source of a binary operator must be of type System.Linq.ParallelQuery<T> rather "
                       + "than System.Collections.Generic.IEnumerable<T>. To fix this problem, use the AsParallel() "
                       + "extension method to convert the right data source to System.Linq.ParallelQuery<T>.")]
    public static bool SequenceEqual<TSource> (this ParallelQuery<TSource> first,
                                                  IEnumerable<TSource> second,
                                                  IEqualityComparer<TSource> comparer)
    {
      throw new NotSupportedException ();
    }

    #endregion
    
    #region GroupBy
    public static ParallelQuery<IGrouping<TKey, TSource>> GroupBy<TSource, TKey> (  this ParallelQuery<TSource> source,
                                                                                  Func<TSource, TKey> keySelector)
    {
      return source.GroupBy (keySelector, EqualityComparer<TKey>.Default);
    }
    
    public static ParallelQuery<IGrouping<TKey, TSource>> GroupBy<TSource, TKey> (  this ParallelQuery<TSource> source,
                                                                                  Func<TSource, TKey> keySelector,
                                                                                  IEqualityComparer<TKey> comparer)
    {
      return source.GroupBy (keySelector, (e) => e, comparer);
    }
    
    public static ParallelQuery<IGrouping<TKey, TElement>> GroupBy<TSource, TKey, TElement> (this ParallelQuery<TSource> source,
                                                                                             Func<TSource, TKey> keySelector,
                                                                                             Func<TSource, TElement> elementSelector)
    {
      return source.GroupBy (keySelector, elementSelector, EqualityComparer<TKey>.Default);
    }
    
    public static ParallelQuery<TResult> GroupBy<TSource, TKey, TResult> (this ParallelQuery<TSource> source,
                                                                          Func<TSource, TKey> keySelector,
                                                                          Func<TKey, IEnumerable<TSource>, TResult> resultSelector)
    {
      return source.GroupBy (keySelector)
        .Select ((g) => resultSelector (g.Key, (IEnumerable<TSource>)g));
    }
    
    public static ParallelQuery<IGrouping<TKey, TElement>> GroupBy<TSource, TKey, TElement> (this ParallelQuery<TSource> source,
                                                                                             Func<TSource, TKey> keySelector,
                                                                                             Func<TSource, TElement> elementSelector,
                                                                                             IEqualityComparer<TKey> comparer)
    {
      throw new NotImplementedException ();
    }
    
    public static ParallelQuery<TResult> GroupBy<TSource, TKey, TElement, TResult> (this ParallelQuery<TSource> source,
                                                                                    Func<TSource, TKey> keySelector,
                                                                                    Func<TSource, TElement> elementSelector,
                                                                                    Func<TKey, IEnumerable<TElement>, TResult> resultSelector)
    {
      return source.GroupBy (keySelector, elementSelector)
        .Select ((g) => resultSelector (g.Key, (IEnumerable<TElement>)g));
    }
    
    public static ParallelQuery<TResult> GroupBy<TSource, TKey, TResult> (  this ParallelQuery<TSource> source,
                                                                          Func<TSource, TKey> keySelector,
                                                                          Func<TKey, IEnumerable<TSource>, TResult> resultSelector,
                                                                          IEqualityComparer<TKey> comparer)
    {
      return source.GroupBy (keySelector, comparer)
        .Select ((g) => resultSelector (g.Key, (IEnumerable<TSource>)g));
    }
    
    public static ParallelQuery<TResult> GroupBy<TSource, TKey, TElement, TResult> (this ParallelQuery<TSource> source,
                                                                                    Func<TSource, TKey> keySelector,
                                                                                    Func<TSource, TElement> elementSelector,
                                                                                    Func<TKey, IEnumerable<TElement>, TResult> resultSelector,
                                                                                    IEqualityComparer<TKey> comparer)
    {
      return source.GroupBy (keySelector, elementSelector, comparer)
        .Select ((g) => resultSelector (g.Key, (IEnumerable<TElement>)g));
    }
    #endregion

    #region GroupJoin
    public static ParallelQuery<TResult> GroupJoin<TOuter, TInner, TKey, TResult> (this ParallelQuery<TOuter> outer,
                                                                                   ParallelQuery<TInner> inner,
                                                                                   Func<TOuter, TKey> outerKeySelector,
                                                                                   Func<TInner, TKey> innerKeySelector,
                                                                                   Func<TOuter, IEnumerable<TInner>, TResult> resultSelector)
    {
      return outer.GroupJoin (inner, outerKeySelector, innerKeySelector, resultSelector, EqualityComparer<TKey>.Default);
    }
    
    public static ParallelQuery<TResult> GroupJoin<TOuter, TInner, TKey, TResult> (this ParallelQuery<TOuter> outer,
                                                                                   ParallelQuery<TInner> inner,
                                                                                   Func<TOuter, TKey> outerKeySelector,
                                                                                   Func<TInner, TKey> innerKeySelector,
                                                                                   Func<TOuter, IEnumerable<TInner>, TResult> resultSelector,
                                                                                   IEqualityComparer<TKey> comparer)
    {
      throw new NotImplementedException ();
    }
    
    [ObsoleteAttribute("The second data source of a binary operator must be of type System.Linq.ParallelQuery<T> rather "
                       + "than System.Collections.Generic.IEnumerable<T>. To fix this problem, use the AsParallel() "
                       + "extension method to convert the right data source to System.Linq.ParallelQuery<T>.")]
    public static ParallelQuery<TResult> GroupJoin<TOuter, TInner, TKey, TResult> (this ParallelQuery<TOuter> outer,
                                                                                   IEnumerable<TInner> inner,
                                                                                   Func<TOuter, TKey> outerKeySelector,
                                                                                   Func<TInner, TKey> innerKeySelector,
                                                                                   Func<TOuter, IEnumerable<TInner>, TResult> resultSelector)
    {
      throw new NotSupportedException ();
    }
    
    [ObsoleteAttribute("The second data source of a binary operator must be of type System.Linq.ParallelQuery<T> rather "
                       + "than System.Collections.Generic.IEnumerable<T>. To fix this problem, use the AsParallel() "
                       + "extension method to convert the right data source to System.Linq.ParallelQuery<T>.")]
    public static ParallelQuery<TResult> GroupJoin<TOuter, TInner, TKey, TResult> (this ParallelQuery<TOuter> outer,
                                                                                   IEnumerable<TInner> inner,
                                                                                   Func<TOuter, TKey> outerKeySelector,
                                                                                   Func<TInner, TKey> innerKeySelector,
                                                                                   Func<TOuter, IEnumerable<TInner>, TResult> resultSelector,
                                                                                   IEqualityComparer<TKey> comparer)
    {
      throw new NotImplementedException ();
    }
    #endregion

    #region ElementAt
    public static TSource ElementAt<TSource> (  this ParallelQuery<TSource> source, int index)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (index < 0)
        throw new ArgumentOutOfRangeException ("index");
      if (index == 0) {
        try {
          return source.First ();
        } catch (InvalidOperationException) {
          throw new ArgumentOutOfRangeException ("index");
        }
      }

      TSource result = default (TSource);

      ParallelQuery<TSource> innerQuery = source.Where ((e, i) => i == index);

      try {
        result = innerQuery.First ();
      } catch (InvalidOperationException) {
        throw new ArgumentOutOfRangeException ("index");
      }

      return result;
    }

    public static TSource ElementAtOrDefault<TSource> (this ParallelQuery<TSource> source, int index)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      try {
        return source.ElementAt (index);
      } catch (ArgumentOutOfRangeException) {
        return default (TSource);
      }
    }
    #endregion

    #region Intersect
    public static ParallelQuery<TSource> Intersect<TSource> (this ParallelQuery<TSource> first,
                                                             ParallelQuery<TSource> second)
    {
      return Intersect<TSource> (first, second, EqualityComparer<TSource>.Default);
    }

    public static ParallelQuery<TSource> Intersect<TSource> (this ParallelQuery<TSource> first,
                                                             ParallelQuery<TSource> second,
                                                             IEqualityComparer<TSource> comparer)
    {
      if (first == null)
        throw new ArgumentNullException ("first");
      if (second == null)
        throw new ArgumentNullException ("second");
      if (comparer == null)
        throw new ArgumentNullException ("comparer");

      return new ParallelQuery<TSource> (new QuerySetNode<TSource> (SetInclusionDefaults.Intersect, comparer, first.Node, second.Node));
    }

    [ObsoleteAttribute("The second data source of a binary operator must be of type System.Linq.ParallelQuery<T> rather "
                       + "than System.Collections.Generic.IEnumerable<T>. To fix this problem, use the AsParallel() "
                       + "extension method to convert the right data source to System.Linq.ParallelQuery<T>.")]
    public static ParallelQuery<TSource> Intersect<TSource> (this ParallelQuery<TSource> first, IEnumerable<TSource> second)
    {
      throw new NotSupportedException ();
    }

    [ObsoleteAttribute("The second data source of a binary operator must be of type System.Linq.ParallelQuery<T> rather "
                       + "than System.Collections.Generic.IEnumerable<T>. To fix this problem, use the AsParallel() "
                       + "extension method to convert the right data source to System.Linq.ParallelQuery<T>.")]
    public static ParallelQuery<TSource> Intersect<TSource> (this ParallelQuery<TSource> first,
                                                             IEnumerable<TSource> second,
                                                             IEqualityComparer<TSource> comparer)
    {
      throw new NotSupportedException ();
    }
    #endregion

    #region Join
    public static ParallelQuery<TResult> Join<TOuter, TInner, TKey, TResult> (  this ParallelQuery<TOuter> outer,
                                                                              ParallelQuery<TInner> inner,
                                                                              Func<TOuter, TKey> outerKeySelector,
                                                                              Func<TInner, TKey> innerKeySelector,
                                                                              Func<TOuter, TInner, TResult> resultSelector)
    {
      return outer.Join (inner, outerKeySelector, innerKeySelector, resultSelector, EqualityComparer<TKey>.Default);
    }
    
    public static ParallelQuery<TResult> Join<TOuter, TInner, TKey, TResult> (  this ParallelQuery<TOuter> outer,
                                                                              ParallelQuery<TInner> inner,
                                                                              Func<TOuter, TKey> outerKeySelector,
                                                                              Func<TInner, TKey> innerKeySelector,
                                                                              Func<TOuter, TInner, TResult> resultSelector,
                                                                              IEqualityComparer<TKey> comparer)
    {
      throw new NotImplementedException ();
    }
    
    [ObsoleteAttribute("The second data source of a binary operator must be of type System.Linq.ParallelQuery<T> rather "
                       + "than System.Collections.Generic.IEnumerable<T>. To fix this problem, use the AsParallel() "
                       + "extension method to convert the right data source to System.Linq.ParallelQuery<T>.")]
    public static ParallelQuery<TResult> Join<TOuter, TInner, TKey, TResult> (  this ParallelQuery<TOuter> outer,
                                                                              IEnumerable<TInner> inner,
                                                                              Func<TOuter, TKey> outerKeySelector,
                                                                              Func<TInner, TKey> innerKeySelector,
                                                                              Func<TOuter, TInner, TResult> resultSelector)
    {
      throw new NotSupportedException ();
    }

    [ObsoleteAttribute("The second data source of a binary operator must be of type System.Linq.ParallelQuery<T> rather "
                       + "than System.Collections.Generic.IEnumerable<T>. To fix this problem, use the AsParallel() "
                       + "extension method to convert the right data source to System.Linq.ParallelQuery<T>.")]
    public static ParallelQuery<TResult> Join<TOuter, TInner, TKey, TResult> (this ParallelQuery<TOuter> outer,
                                                                              IEnumerable<TInner> inner,
                                                                              Func<TOuter, TKey> outerKeySelector,
                                                                              Func<TInner, TKey> innerKeySelector,
                                                                              Func<TOuter, TInner, TResult> resultSelector,
                                                                              IEqualityComparer<TKey> comparer)
    {
      throw new NotSupportedException ();
    }
    #endregion

    #region Except
    public static ParallelQuery<TSource> Except<TSource> (  this ParallelQuery<TSource> first,
                                                          ParallelQuery<TSource> second)
    {
      return Except<TSource> (first, second, EqualityComparer<TSource>.Default);
    }

    public static ParallelQuery<TSource> Except<TSource> (  this ParallelQuery<TSource> first,
                                                          ParallelQuery<TSource> second,
                                                          IEqualityComparer<TSource> comparer)
    {
      if (first == null)
        throw new ArgumentNullException ("first");
      if (second == null)
        throw new ArgumentNullException ("second");
      if (comparer == null)
        throw new ArgumentNullException ("comparer");

      return new ParallelQuery<TSource> (new QuerySetNode<TSource> (SetInclusionDefaults.Except,
                                                                    comparer, first.Node, second.Node));
    }

    [ObsoleteAttribute("The second data source of a binary operator must be of type System.Linq.ParallelQuery<T> rather "
                       + "than System.Collections.Generic.IEnumerable<T>. To fix this problem, use the AsParallel() "
                       + "extension method to convert the right data source to System.Linq.ParallelQuery<T>.")]
    public static ParallelQuery<TSource> Except<TSource> (this ParallelQuery<TSource> first,
                                                          IEnumerable<TSource> second)
    {
      throw new NotSupportedException ();
    }

    [ObsoleteAttribute("The second data source of a binary operator must be of type System.Linq.ParallelQuery<T> rather "
                       + "than System.Collections.Generic.IEnumerable<T>. To fix this problem, use the AsParallel() "
                       + "extension method to convert the right data source to System.Linq.ParallelQuery<T>.")]
    public static ParallelQuery<TSource> Except<TSource> (  this ParallelQuery<TSource> first,
                                                          IEnumerable<TSource> second,
                                                          IEqualityComparer<TSource> comparer)
    {
      throw new NotSupportedException ();
    }
    #endregion

    #region Distinct
    public static ParallelQuery<TSource> Distinct<TSource> (this ParallelQuery<TSource> source)
    {
      return Distinct<TSource> (source, EqualityComparer<TSource>.Default);
    }

    public static ParallelQuery<TSource> Distinct<TSource> (this ParallelQuery<TSource> source, IEqualityComparer<TSource> comparer)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (comparer == null)
        throw new ArgumentNullException ("comparer");

      return new ParallelQuery<TSource> (new QuerySetNode<TSource> (SetInclusionDefaults.Distinct, comparer,
                                                                    source.Node, null));
    }
    #endregion

    #region Union
    [ObsoleteAttribute("The second data source of a binary operator must be of type System.Linq.ParallelQuery<T> rather "
                       + "than System.Collections.Generic.IEnumerable<T>. To fix this problem, use the AsParallel() "
                       + "extension method to convert the right data source to System.Linq.ParallelQuery<T>.")]
    public static ParallelQuery<TSource> Union<TSource> (this ParallelQuery<TSource> first,
                                                         IEnumerable<TSource> second)
    {
      throw new NotSupportedException ();
    }

    [ObsoleteAttribute("The second data source of a binary operator must be of type System.Linq.ParallelQuery<T> rather "
                       + "than System.Collections.Generic.IEnumerable<T>. To fix this problem, use the AsParallel() "
                       + "extension method to convert the right data source to System.Linq.ParallelQuery<T>.")]
    public static ParallelQuery<TSource> Union<TSource>(this ParallelQuery<TSource> first,
                                                        IEnumerable<TSource> second,
                                                        IEqualityComparer<TSource> comparer)
    {
      throw new NotSupportedException ();
    }

    public static ParallelQuery<TSource> Union<TSource> (this ParallelQuery<TSource> first,
                                                         ParallelQuery<TSource> second)
    {
      return first.Union (second, EqualityComparer<TSource>.Default);
    }

    public static ParallelQuery<TSource> Union<TSource> (this ParallelQuery<TSource> first,
                                                         ParallelQuery<TSource> second,
                                                         IEqualityComparer<TSource> comparer)
    {
      if (first == null)
        throw new ArgumentNullException ("first");
      if (second == null)
        throw new ArgumentNullException ("second");
      if (comparer == null)
        throw new ArgumentNullException ("comparer");

      return new ParallelQuery<TSource> (new QuerySetNode<TSource> (SetInclusionDefaults.Union, comparer, first.Node, second.Node));
    }
    #endregion

    #region Take
    // TODO : introduce some early break up here, use ImplementerToken
    public static ParallelQuery<TSource> Take<TSource> (this ParallelQuery<TSource> source, int count)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Where ((e, i) => i < count);
    }

    public static ParallelQuery<TSource> TakeWhile<TSource> (this ParallelQuery<TSource> source,
                                                             Func<TSource, bool> predicate)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (predicate == null)
        throw new ArgumentNullException ("predicate");

      return source.Where ((e) => predicate (e));
    }

    public static ParallelQuery<TSource> TakeWhile<TSource> (this ParallelQuery<TSource> source,
                                                             Func<TSource, int, bool> predicate)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (predicate == null)
        throw new ArgumentNullException ("predicate");

      return source.Where ((e, i) => predicate (e, i));
    }
    #endregion

    #region Skip
    public static ParallelQuery<TSource> Skip<TSource> (this ParallelQuery<TSource> source, int count)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Where ((e, i) => i >= count);
    }

    public static ParallelQuery<TSource> SkipWhile<TSource> (this ParallelQuery<TSource> source,
                                                             Func<TSource, bool> predicate)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (predicate == null)
        throw new ArgumentNullException ("predicate");

      return source.Where ((e) => !predicate (e));
    }

    public static ParallelQuery<TSource> SkipWhile<TSource> (this ParallelQuery<TSource> source,
                                                             Func<TSource, int, bool> predicate)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (predicate == null)
        throw new ArgumentNullException ("predicate");

      return source.Where ((e, i) => !predicate (e, i));
    }
    #endregion

    #region Single
    static TSource SingleInternal<TSource> (this ParallelQuery<TSource> source, params TSource[] init)
    {
      TSource result = default(TSource);
      bool hasValue = false;

      foreach (TSource element in source) {
        if (hasValue)
          throw new InvalidOperationException ("The input sequence contains more than one element.");

        result = element;
        hasValue = true;
      }

      if (!hasValue && init.Length != 0) {
        result = init[0];
        hasValue = true;
      }

      if (!hasValue)
        throw new InvalidOperationException ("The input sequence is empty.");

      return result;
    }

    public static TSource Single<TSource> (this ParallelQuery<TSource> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return SingleInternal<TSource> (source);
    }

    public static TSource Single<TSource> (this ParallelQuery<TSource> source,
                                           Func<TSource, bool> predicate)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (predicate == null)
        throw new ArgumentNullException ("predicate");

      return source.Where (predicate).Single ();
    }

    public static TSource SingleOrDefault<TSource> (this ParallelQuery<TSource> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return SingleInternal<TSource> (source, default (TSource));
    }

    public static TSource SingleOrDefault<TSource> (this ParallelQuery<TSource> source, Func<TSource, bool> predicate)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (predicate == null)
        throw new ArgumentNullException ("predicate");

      return source.Where (predicate).SingleOrDefault ();
    }
    #endregion

    #region Count
    public static int Count<TSource> (this ParallelQuery<TSource> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Aggregate<TSource, int, int> (() => 0,
                                                 (acc, e) => acc + 1,
                                                 (acc1, acc2) => acc1 + acc2,
                                                 (result) => result);
    }

    public static int Count<TSource> (this ParallelQuery<TSource> source, Func<TSource, bool> predicate)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (predicate == null)
        throw new ArgumentNullException ("predicate");

      return source.Where (predicate).Count ();
    }

    public static long LongCount<TSource> (this ParallelQuery<TSource> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Aggregate<TSource, long, long> (() => 0,
                                                    (acc, e) => acc + 1,
                                                    (acc1, acc2) => acc1 + acc2,
                                                    (result) => result);
    }

    public static long LongCount<TSource> (this ParallelQuery<TSource> source, Func<TSource, bool> predicate)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (predicate == null)
        throw new ArgumentNullException ("predicate");

      return source.Where (predicate).LongCount ();
    }
    #endregion

    #region Average
    public static double Average (this ParallelQuery<int> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Aggregate (() => new int[2],
                              (acc, e) => { acc[0] += e; acc[1]++; return acc; },
                              (acc1, acc2) => { acc1[0] += acc2[0]; acc1[1] += acc2[1]; return acc1; },
                              (acc) => acc[0] / ((double)acc[1]));
    }

    public static double Average (this ParallelQuery<long> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Aggregate (() => new long[2],
                              (acc, e) => { acc[0] += e; acc[1]++; return acc; },
                              (acc1, acc2) => { acc1[0] += acc2[0]; acc1[1] += acc2[1]; return acc1; },
                              (acc) => acc[0] / ((double)acc[1]));
    }

    public static decimal Average (this ParallelQuery<decimal> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Aggregate (() => new decimal[2],
                              (acc, e) => { acc[0] += e; acc[1]++; return acc; },
                              (acc1, acc2) => { acc1[0] += acc2[0]; acc1[1] += acc2[1]; return acc1; },
                              (acc) => acc[0] / acc[1]);
    }

    public static double Average (this ParallelQuery<double> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Aggregate (() => new double[2],
                              (acc, e) => { acc[0] += e; acc[1]++; return acc; },
                              (acc1, acc2) => { acc1[0] += acc2[0]; acc1[1] += acc2[1]; return acc1; },
                              (acc) => acc[0] / ((double)acc[1]));
    }

    public static float Average (this ParallelQuery<float> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Aggregate (() => new float[2],
                              (acc, e) => { acc[0] += e; acc[1]++; return acc; },
                              (acc1, acc2) => { acc1[0] += acc2[0]; acc1[1] += acc2[1]; return acc1; },
                              (acc) => acc[0] / acc[1]);
    }
    #endregion

    #region More Average
    public static double? Average (this ParallelQuery<int?> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Select ((e) => e.HasValue ? e.Value : 0).Average ();;
    }

    public static double? Average (this ParallelQuery<long?> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Select ((e) => e.HasValue ? e.Value : 0).Average ();
    }

    public static decimal? Average (this ParallelQuery<decimal?> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Select ((e) => e.HasValue ? e.Value : 0).Average ();
    }

    public static double? Average (this ParallelQuery<double?> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Select ((e) => e.HasValue ? e.Value : 0).Average ();
    }

    public static float? Average (this ParallelQuery<float?> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Select ((e) => e.HasValue ? e.Value : 0).Average ();
    }

    public static double Average<TSource> (this ParallelQuery<TSource> source, Func<TSource, int> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Average ();
    }

    public static double Average<TSource> (this ParallelQuery<TSource> source, Func<TSource, long> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Average ();
    }

    public static float Average<TSource> (this ParallelQuery<TSource> source, Func<TSource, float> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Average ();
    }

    public static double Average<TSource> (this ParallelQuery<TSource> source, Func<TSource, double> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Average ();
    }

    public static decimal Average<TSource> (this ParallelQuery<TSource> source, Func<TSource, decimal> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Average ();
    }

    public static double? Average<TSource> (this ParallelQuery<TSource> source, Func<TSource, int?> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Average ();
    }

    public static double? Average<TSource> (this ParallelQuery<TSource> source, Func<TSource, long?> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Average ();
    }

    public static float? Average<TSource> (this ParallelQuery<TSource> source, Func<TSource, float?> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Average ();
    }

    public static double? Average<TSource> (this ParallelQuery<TSource> source, Func<TSource, double?> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Average ();
    }

    public static decimal? Average<TSource> (this ParallelQuery<TSource> source, Func<TSource, decimal?> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Average ();
    }
    #endregion

    #region Sum
    public static int Sum (this ParallelQuery<int> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Aggregate (0, (e1, e2) => e1 + e2, (sum1, sum2) => sum1 + sum2, (sum) => sum);
    }

    public static long Sum (this ParallelQuery<long> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Aggregate ((long)0, (e1, e2) => e1 + e2, (sum1, sum2) => sum1 + sum2, (sum) => sum);
    }

    public static float Sum (this ParallelQuery<float> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Aggregate (0.0f, (e1, e2) => e1 + e2, (sum1, sum2) => sum1 + sum2, (sum) => sum);
    }

    public static double Sum (this ParallelQuery<double> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Aggregate (0.0, (e1, e2) => e1 + e2, (sum1, sum2) => sum1 + sum2, (sum) => sum);
    }

    public static decimal Sum (this ParallelQuery<decimal> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Aggregate ((decimal)0, (e1, e2) => e1 + e2, (sum1, sum2) => sum1 + sum2, (sum) => sum);
    }

    public static int? Sum (this ParallelQuery<int?> source)
    {
      return source.Select ((e) => e.HasValue ? e.Value : 0).Sum ();
    }

    public static long? Sum (this ParallelQuery<long?> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Select ((e) => e.HasValue ? e.Value : 0).Sum ();
    }

    public static float? Sum (this ParallelQuery<float?> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Select ((e) => e.HasValue ? e.Value : 0).Sum ();
    }

    public static double? Sum (this ParallelQuery<double?> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Select ((e) => e.HasValue ? e.Value : 0).Sum ();
    }

    public static decimal? Sum (this ParallelQuery<decimal?> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Select ((e) => e.HasValue ? e.Value : 0).Sum ();
    }

    public static int Sum<TSource> (this ParallelQuery<TSource> source, Func<TSource, int> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Sum ();
    }

    public static long Sum<TSource> (this ParallelQuery<TSource> source, Func<TSource, long> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Sum ();
    }

    public static decimal Sum<TSource> (this ParallelQuery<TSource> source, Func<TSource, decimal> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Sum ();
    }

    public static float Sum<TSource> (this ParallelQuery<TSource> source, Func<TSource, float> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Sum ();
    }

    public static double Sum<TSource> (this ParallelQuery<TSource> source, Func<TSource, double> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Sum ();
    }

    public static int? Sum<TSource> (this ParallelQuery<TSource> source, Func<TSource, int?> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Sum ();
    }

    public static long? Sum<TSource> (this ParallelQuery<TSource> source, Func<TSource, long?> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Sum ();
    }

    public static decimal? Sum<TSource> (this ParallelQuery<TSource> source, Func<TSource, decimal?> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Sum ();
    }

    public static float? Sum<TSource> (this ParallelQuery<TSource> source, Func<TSource, float?> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Sum ();
    }

    public static double? Sum<TSource> (this ParallelQuery<TSource> source, Func<TSource, double?> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Sum ();
    }
    #endregion

    #region Min-Max
    static T BestOrder<T> (ParallelQuery<T> source, Func<T, T, bool> bestSelector, T seed)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      T best = seed;

      best = source.Aggregate (() => seed,
                              (first, second) => (bestSelector(first, second)) ? first : second,
                              (first, second) => (bestSelector(first, second)) ? first : second,
                              (e) => e);
      return best;
    }

    public static int Min (this ParallelQuery<int> source)
    {
      return BestOrder (source, (first, second) => first < second, int.MaxValue);
    }

    public static long Min (this ParallelQuery<long> source)
    {
      return BestOrder (source, (first, second) => first < second, long.MaxValue);
    }

    public static float Min (this ParallelQuery<float> source)
    {
      return BestOrder (source, (first, second) => first < second, float.MaxValue);
    }

    public static double Min (this ParallelQuery<double> source)
    {
      return BestOrder (source, (first, second) => first < second, double.MaxValue);
    }

    public static decimal Min (this ParallelQuery<decimal> source)
    {
      return BestOrder (source, (first, second) => first < second, decimal.MaxValue);
    }

    public static TSource Min<TSource> (this ParallelQuery<TSource> source)
    {
      IComparer<TSource> comparer = Comparer<TSource>.Default;

      return BestOrder (source, (first, second) => comparer.Compare (first, second) < 0, default (TSource));
    }

    public static TResult Min<TSource, TResult> (this ParallelQuery<TSource> source, Func<TSource, TResult> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Min ();
    }

    public static int? Min (this ParallelQuery<int?> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Select ((e) => e.HasValue ? e.Value : int.MaxValue).Min ();
    }

    public static long? Min (this ParallelQuery<long?> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Select ((e) => e.HasValue ? e.Value : long.MaxValue).Min ();
    }

    public static float? Min (this ParallelQuery<float?> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Select ((e) => e.HasValue ? e.Value : float.MaxValue).Min ();
    }

    public static double? Min (this ParallelQuery<double?> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Select ((e) => e.HasValue ? e.Value : double.MaxValue).Min ();
    }

    public static decimal? Min (this ParallelQuery<decimal?> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Select ((e) => e.HasValue ? e.Value : decimal.MaxValue).Min ();
    }

    public static int Min<TSource> (this ParallelQuery<TSource> source, Func<TSource, int> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Min ();
    }

    public static long Min<TSource> (this ParallelQuery<TSource> source, Func<TSource, long> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Min ();
    }

    public static float Min<TSource> (this ParallelQuery<TSource> source, Func<TSource, float> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Min ();
    }

    public static double Min<TSource> (this ParallelQuery<TSource> source, Func<TSource, double> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Min ();
    }

    public static decimal Min<TSource> (this ParallelQuery<TSource> source, Func<TSource, decimal> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Min ();
    }

    public static int? Min<TSource> (this ParallelQuery<TSource> source, Func<TSource, int?> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Min ();
    }

    public static long? Min<TSource> (this ParallelQuery<TSource> source, Func<TSource, long?> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Min ();
    }

    public static float? Min<TSource> (this ParallelQuery<TSource> source, Func<TSource, float?> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Min ();
    }

    public static double? Min<TSource> (this ParallelQuery<TSource> source, Func<TSource, double?> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Min ();
    }

    public static decimal? Min<TSource> (this ParallelQuery<TSource> source, Func<TSource, decimal?> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Min ();
    }

    public static int Max (this ParallelQuery<int> source)
    {
      return BestOrder (source, (first, second) => first > second, int.MinValue);
    }

    public static long Max(this ParallelQuery<long> source)
    {
      return BestOrder(source, (first, second) => first > second, long.MinValue);
    }

    public static float Max (this ParallelQuery<float> source)
    {
      return BestOrder(source, (first, second) => first > second, float.MinValue);
    }

    public static double Max (this ParallelQuery<double> source)
    {
      return BestOrder(source, (first, second) => first > second, double.MinValue);
    }

    public static decimal Max (this ParallelQuery<decimal> source)
    {
      return BestOrder(source, (first, second) => first > second, decimal.MinValue);
    }

    public static TSource Max<TSource> (this ParallelQuery<TSource> source)
    {
      IComparer<TSource> comparer = Comparer<TSource>.Default;

      return BestOrder (source, (first, second) => comparer.Compare (first, second) > 0, default (TSource));
    }

    public static TResult Max<TSource, TResult> (this ParallelQuery<TSource> source, Func<TSource, TResult> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Max ();
    }

    public static int? Max (this ParallelQuery<int?> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Select ((e) => e.HasValue ? e.Value : int.MinValue).Max ();
    }

    public static long? Max (this ParallelQuery<long?> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Select ((e) => e.HasValue ? e.Value : long.MinValue).Max ();
    }

    public static float? Max (this ParallelQuery<float?> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Select ((e) => e.HasValue ? e.Value : float.MinValue).Max ();
    }

    public static double? Max (this ParallelQuery<double?> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Select ((e) => e.HasValue ? e.Value : double.MinValue).Max ();
    }

    public static decimal? Max (this ParallelQuery<decimal?> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.Select ((e) => e.HasValue ? e.Value : decimal.MinValue).Max ();
    }

    public static int Max<TSource> (this ParallelQuery<TSource> source, Func<TSource, int> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Max ();
    }

    public static long Max<TSource> (this ParallelQuery<TSource> source, Func<TSource, long> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Max ();
    }

    public static float Max<TSource> (this ParallelQuery<TSource> source, Func<TSource, float> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Max ();
    }

    public static double Max<TSource> (this ParallelQuery<TSource> source, Func<TSource, double> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Max ();
    }

    public static decimal Max<TSource> (this ParallelQuery<TSource> source, Func<TSource, decimal> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Max ();
    }

    public static int? Max<TSource> (this ParallelQuery<TSource> source, Func<TSource, int?> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Max ();
    }

    public static long? Max<TSource> (this ParallelQuery<TSource> source, Func<TSource, long?> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Max ();
    }

    public static float? Max<TSource> (this ParallelQuery<TSource> source, Func<TSource, float?> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Max ();
    }

    public static double? Max<TSource> (this ParallelQuery<TSource> source, Func<TSource, double?> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Max ();
    }

    public static decimal? Max<TSource> (this ParallelQuery<TSource> source, Func<TSource, decimal?> func)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (func == null)
        throw new ArgumentNullException ("func");

      return source.Select (func).Max ();
    }
    #endregion

    #region Cast / OfType
    public static ParallelQuery<TResult> Cast<TResult> (this ParallelQuery source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.TypedQuery.Select ((e) => (TResult)e);
    }

    public static ParallelQuery<TResult> OfType<TResult> (this ParallelQuery source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return source.TypedQuery.Where ((e) => e is TResult).Cast<TResult> ();
    }
    #endregion

    #region Reverse
    public static ParallelQuery<TSource> Reverse<TSource> (this ParallelQuery<TSource> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      return new ParallelQuery<TSource> (new QueryReverseNode<TSource> (source));
    }
    #endregion

    #region ToArray - ToList - ToDictionary - ToLookup
    public static List<TSource> ToList<TSource> (this ParallelQuery<TSource> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      OrderedParallelQuery<TSource> ordered = null;
      if ((ordered = source as OrderedParallelQuery<TSource>) != null)
        return ToListOrdered (ordered);

      List<TSource> temp = source.Aggregate (() => new List<TSource>(50),
                                             (list, e) => { list.Add (e); return list; },
                                             (list, list2) => { list.AddRange (list2); return list; },
                                             (list) => list);
      return temp;
    }

    static List<TSource> ToListOrdered<TSource> (this OrderedParallelQuery<TSource> source)
    {
      List<TSource> result = new List<TSource> ();

      foreach (TSource element in source)
        result.Add (element);

      return result;
    }

    public static TSource[] ToArray<TSource> (this ParallelQuery<TSource> source)
    {
      if (source == null)
        throw new ArgumentNullException ("source");

      TSource[] result = null;

      Func<List<TSource>, TSource, List<TSource>> intermediate = (list, e) => {
        list.Add (e); return list;
      };

      Action<IList<List<TSource>>> final = (list) => {
        int count = 0;

        for (int i = 0; i < list.Count; i++)
          count += list[i].Count;

        result = new TSource[count];
        int insertIndex = -1;

        for (int i = 0; i < list.Count; i++)
          for (int j = 0; j < list[i].Count; j++)
            result [++insertIndex] = list[i][j];
      };

      ParallelExecuter.ProcessAndAggregate<TSource, List<TSource>> (source.Node,
                                                                    () => new List<TSource> (),
                                                                    intermediate,
                                                                    final);

      return result;
    }

    public static Dictionary<TKey, TSource> ToDictionary<TSource, TKey> (this ParallelQuery<TSource> source,
                                                                         Func<TSource, TKey> keySelector,
                                                                         IEqualityComparer<TKey> comparer)
    {
      return ToDictionary<TSource, TKey, TSource> (source, keySelector, (e) => e, comparer);
    }

    public static Dictionary<TKey, TSource> ToDictionary<TSource, TKey> (this ParallelQuery<TSource> source,
                                                                         Func<TSource, TKey> keySelector)
    {
      return ToDictionary<TSource, TKey, TSource> (source, keySelector, (e) => e, EqualityComparer<TKey>.Default);
    }

    public static Dictionary<TKey, TElement> ToDictionary<TSource, TKey, TElement> (this ParallelQuery<TSource> source,
                                                                                      Func<TSource, TKey> keySelector,
                                                                                      Func<TSource, TElement> elementSelector)
    {
      return ToDictionary<TSource, TKey, TElement> (source, keySelector, elementSelector, EqualityComparer<TKey>.Default);
    }

    public static Dictionary<TKey, TElement> ToDictionary<TSource, TKey, TElement> (this ParallelQuery<TSource> source,
                                                                                      Func<TSource, TKey> keySelector,
                                                                                      Func<TSource, TElement> elementSelector,
                                                                                      IEqualityComparer<TKey> comparer)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (keySelector == null)
        throw new ArgumentNullException ("keySelector");
      if (comparer == null)
        throw new ArgumentNullException ("comparer");
      if (elementSelector == null)
        throw new ArgumentNullException ("elementSelector");

      return source.Aggregate (() => new Dictionary<TKey, TElement> (comparer),
                                (d, e) => { d.Add (keySelector (e), elementSelector (e)); return d; },
                                (d1, d2) => { foreach (var couple in d2) d1.Add (couple.Key, couple.Value); return d1; },
                                (d) => d);
    }

    public static ILookup<TKey, TSource> ToLookup<TSource, TKey> (  this ParallelQuery<TSource> source,
                                                                  Func<TSource, TKey> keySelector)
    {
      return ToLookup<TSource, TKey, TSource> (source, keySelector, (e) => e, EqualityComparer<TKey>.Default);
    }

    public static ILookup<TKey, TSource> ToLookup<TSource, TKey> (  this ParallelQuery<TSource> source,
                                                                  Func<TSource, TKey> keySelector,
                                                                  IEqualityComparer<TKey> comparer)
    {
      return ToLookup<TSource, TKey, TSource> (source, keySelector, (e) => e, comparer);
    }

    public static ILookup<TKey, TElement> ToLookup<TSource, TKey, TElement> (this ParallelQuery<TSource> source,
                                                                             Func<TSource, TKey> keySelector,
                                                                             Func<TSource, TElement> elementSelector)
    {
      return ToLookup<TSource, TKey, TElement> (source, keySelector, elementSelector, EqualityComparer<TKey>.Default);
    }

    public static ILookup<TKey, TElement> ToLookup<TSource, TKey, TElement> (this ParallelQuery<TSource> source,
                                                                             Func<TSource, TKey> keySelector,
                                                                             Func<TSource, TElement> elementSelector,
                                                                             IEqualityComparer<TKey> comparer)
    {
      if (source == null)
        throw new ArgumentNullException ("source");
      if (keySelector == null)
        throw new ArgumentNullException ("keySelector");
      if (comparer == null)
        throw new ArgumentNullException ("comparer");
      if (elementSelector == null)
        throw new ArgumentNullException ("elementSelector");

      ConcurrentLookup<TKey, TElement> lookup = new ConcurrentLookup<TKey, TElement> (comparer);
      source.ForAll ((e) => lookup.Add (keySelector (e), elementSelector (e)));

      return lookup;
    }
    #endregion

    #region Concat
    [ObsoleteAttribute("The second data source of a binary operator must be of type System.Linq.ParallelQuery<T> rather than "
                       + "System.Collections.Generic.IEnumerable<T>. To fix this problem, use the AsParallel() extension method "
                       + "to convert the right data source to System.Linq.ParallelQuery<T>.")]
    public static ParallelQuery<TSource> Concat<TSource>(this ParallelQuery<TSource> first,
                                                         IEnumerable<TSource> second)
    {
      throw new NotSupportedException ();
    }

    public static ParallelQuery<TSource> Concat<TSource> (  this ParallelQuery<TSource> first, ParallelQuery<TSource> second)
    {
      return new ParallelQuery<TSource> (new QueryConcatNode<TSource> (first.Node, second.Node));
    }
    #endregion
    
    #region DefaultIfEmpty
    public static ParallelQuery<TSource> DefaultIfEmpty<TSource> (  this ParallelQuery<TSource> source)
    {
      return source.DefaultIfEmpty (default (TSource));
    }
    
    public static ParallelQuery<TSource> DefaultIfEmpty<TSource> (  this ParallelQuery<TSource> source, TSource defaultValue)
    {
      return new ParallelQuery<TSource> (new QueryDefaultEmptyNode<TSource> (source.Node, defaultValue));
    }
    #endregion
    
    #region First
    public static TSource First<TSource> (  this ParallelQuery<TSource> source)
    {
      CancellationTokenSource src = new CancellationTokenSource ();
      IEnumerator<TSource> enumerator = source.WithImplementerToken (src).GetEnumerator ();
      
      if (enumerator == null || !enumerator.MoveNext ())
        throw new InvalidOperationException ("source contains no element");
      
      TSource result = enumerator.Current;
      src.Cancel ();
      
      return result;
    }
    
    public static TSource First<TSource> (  this ParallelQuery<TSource> source, Func<TSource, bool> predicate)
    {
      return source.Where (predicate).First ();
    }
    
    public static TSource FirstOrDefault<TSource> (this ParallelQuery<TSource> source)
    {
      return source.DefaultIfEmpty ().First ();
    }
    
    public static TSource FirstOrDefault<TSource> (this ParallelQuery<TSource> source, Func<TSource, bool> predicate)
    {
      return source.Where (predicate).FirstOrDefault ();
    }
    #endregion
    
    #region Last
    public static TSource Last<TSource> (this ParallelQuery<TSource> source)
    {
      return source.Reverse ().First ();
    }
    
    public static TSource Last<TSource> (  this ParallelQuery<TSource> source, Func<TSource, bool> predicate)
    {
      return source.Reverse ().First (predicate);
    }
    
    public static TSource LastOrDefault<TSource> (this ParallelQuery<TSource> source)
    {
      return source.Reverse ().FirstOrDefault ();
    }
    
    public static TSource LastOrDefault<TSource> (this ParallelQuery<TSource> source, Func<TSource, bool> predicate)
    {
      return source.Reverse ().FirstOrDefault (predicate);
    }
    #endregion

    #region Zip
    public static ParallelQuery<TResult> Zip<TFirst, TSecond, TResult> (this ParallelQuery<TFirst> first,
                                                                          ParallelQuery<TSecond> second,
                                                                          Func<TFirst, TSecond, TResult> resultSelector)
    {
      if (first == null)
        throw new ArgumentNullException ("first");
      if (second == null)
        throw new ArgumentNullException ("second");
      if (resultSelector == null)
        throw new ArgumentNullException ("resultSelector");

      return new ParallelQuery<TResult> (new QueryZipNode<TFirst, TSecond, TResult> (resultSelector, first.Node, second.Node));
    }

    [ObsoleteAttribute("The second data source of a binary operator must be of type System.Linq.ParallelQuery<T> rather "
                       + "than System.Collections.Generic.IEnumerable<T>. To fix this problem, use the AsParallel() "
                       + "extension method to convert the right data source to System.Linq.ParallelQuery<T>.")]
    public static ParallelQuery<TResult> Zip<TFirst, TSecond, TResult> (this ParallelQuery<TFirst> first,
                                                                          IEnumerable<TSecond> second,
                                                                          Func<TFirst, TSecond, TResult> resultSelector)
    {
      throw new NotSupportedException ();
    }
    #endregion
  }
}
#endif
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