prints unique letters from Product and Customer names : Union « LINQ « C# / CSharp Tutorial

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C# / CSharp Tutorial » LINQ » Union 
22.20.4.prints unique letters from Product and Customer names
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

public class MainClass {
    public static void Main() {

        List<Product> products = GetProductList();
        List<Customer> customers = GetCustomerList();

        var productFirstChars =
            from p in products
            select p.ProductName[0];
        var customerFirstChars =
            from c in customers
            select c.CompanyName[0];

        var uniqueFirstChars = productFirstChars.Union(customerFirstChars);

        Console.WriteLine("Unique first letters from Product names and Customer names:");
        foreach (var ch in uniqueFirstChars) {
            Console.WriteLine(ch);
        }
    }
    static List<Product> GetProductList() {
        List<Product> empTree = new List<Product>();
        empTree.Add(new Product ProductName = "A", Category = "O", UnitPrice = 12, UnitsInStock = 5, Total = 36, OrderDate = new DateTime(200511), Id = });
        empTree.Add(new Product ProductName = "B", Category = "O", UnitPrice = 2, UnitsInStock = 4, Total = 35, OrderDate = new DateTime(200511), Id = });
        empTree.Add(new Product ProductName = "C", Category = "O", UnitPrice = 112, UnitsInStock = 3, Total = 34, OrderDate = new DateTime(200511), Id = });
        empTree.Add(new Product ProductName = "D", Category = "O", UnitPrice = 112, UnitsInStock = 0, Total = 33, OrderDate = new DateTime(200511), Id = });
        empTree.Add(new Product ProductName = "E", Category = "O", UnitPrice = 1112, UnitsInStock = 2, Total = 32, OrderDate = new DateTime(200511), Id = });
        empTree.Add(new Product ProductName = "F", Category = "O", UnitPrice = 11112, UnitsInStock = 0, Total = 31, OrderDate = new DateTime(200511), Id = });
        return empTree;
    }
    static List<Customer> GetCustomerList() {
        List<Product> empTree = new List<Product>();
        empTree.Add(new Product ProductName = "A", Category = "O", UnitPrice = 12, UnitsInStock = 5, Total = 36, OrderDate = new DateTime(200511), Id = });
        empTree.Add(new Product ProductName = "B", Category = "O", UnitPrice = 2, UnitsInStock = 4, Total = 35, OrderDate = new DateTime(200511), Id = });
        empTree.Add(new Product ProductName = "C", Category = "O", UnitPrice = 112, UnitsInStock = 3, Total = 34, OrderDate = new DateTime(200511), Id = });
        empTree.Add(new Product ProductName = "D", Category = "O", UnitPrice = 112, UnitsInStock = 0, Total = 33, OrderDate = new DateTime(200511), Id = });
        empTree.Add(new Product ProductName = "E", Category = "O", UnitPrice = 1112, UnitsInStock = 2, Total = 32, OrderDate = new DateTime(200511), Id = });
        empTree.Add(new Product ProductName = "F", Category = "O", UnitPrice = 11112, UnitsInStock = 0, Total = 31, OrderDate = new DateTime(200511), Id = });

        List<Customer> l = new List<Customer>();
        l.Add(new Customer CompanyName = "A", Region = "R1", UnitsInStock = 1, Orders = empTree, CustomerId = });
        l.Add(new Customer CompanyName = "B", Region = "R2", UnitsInStock = 2, Orders = empTree, CustomerId = });
        l.Add(new Customer CompanyName = "C", Region = "R3", UnitsInStock = 3, Orders = empTree, CustomerId = });
        l.Add(new Customer CompanyName = "D", Region = "R4", UnitsInStock = 4, Orders = empTree, CustomerId = });
        l.Add(new Customer CompanyName = "E", Region = "R5", UnitsInStock = 5, Orders = empTree, CustomerId = });
        return l;
    }
}
class Customer : IComparable<Customer> {
    public string CompanyName get; set; }
    public string Region get; set; }
    public List<Product> Orders get; set; }
    public int UnitsInStock get; set; }
    public int CustomerId get; set; }

    public override string ToString() {
        return String.Format("Id: {0}, Name: {1}, Region: {3}"this.CustomerId, this.CompanyName, this.Region);
    }
    int IComparable<Customer>.CompareTo(Customer other) {
        if (other == null)
            return 1;

        if (this.CustomerId > other.CustomerId)
            return 1;

        if (this.CustomerId < other.CustomerId)
            return -1;

        return 0;
    }
}
class Product : IComparable<Product> {
    public string ProductName get; set; }
    public string Category get; set; }
    public int UnitPrice get; set; }
    public int UnitsInStock get; set; }
    public int Total get; set; }
    public DateTime OrderDate get; set; }
    public int Id get; set; }

    public override string ToString() {
        return String.Format("Id: {0}, Name: {1} , Category: {3}"this.Id, this.ProductName, this.Category);
    }
    int IComparable<Product>.CompareTo(Product other) {
        if (other == null)
            return 1;
        if (this.Id > other.Id)
            return 1;

        if (this.Id < other.Id)
            return -1;

        return 0;
    }
}
22.20.Union
22.20.1.Create the Union query
22.20.2.Use Linq to union two arrays
22.20.3.prints the unique elements of two integer arrays
22.20.4.prints unique letters from Product and Customer names
22.20.5.Union Operator
22.20.6.Union does appends one sequence to another with duplicates removed:
22.20.7.Set Operators: Union
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