Source Code Cross Referenced for GroupByIterator.java in  » XML » saxonb » net » sf » saxon » sort » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » XML » saxonb » net.sf.saxon.sort 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        package net.sf.saxon.sort;
002:
003:        import net.sf.saxon.expr.Expression;
004:        import net.sf.saxon.expr.LastPositionFinder;
005:        import net.sf.saxon.expr.XPathContext;
006:        import net.sf.saxon.om.Item;
007:        import net.sf.saxon.om.ListIterator;
008:        import net.sf.saxon.om.SequenceIterator;
009:        import net.sf.saxon.om.LookaheadIterator;
010:        import net.sf.saxon.trace.Location;
011:        import net.sf.saxon.trans.XPathException;
012:        import net.sf.saxon.value.AtomicValue;
013:
014:        import java.util.ArrayList;
015:        import java.util.Comparator;
016:        import java.util.HashMap;
017:        import java.util.List;
018:
019:        /**
020:         * A GroupByIterator iterates over a sequence of groups defined by
021:         * xsl:for-each-group group-by="x". The groups are returned in
022:         * order of first appearance. Note that an item can appear in several groups;
023:         * indeed, an item may be the leading item of more than one group, which means
024:         * that knowing the leading item is not enough to know the current group.
025:         *
026:         * <p>The GroupByIterator acts as a SequenceIterator, where successive calls of
027:         * next() return the leading item of each group in turn. The current item of
028:         * the iterator is therefore the leading item of the current group. To get access
029:         * to all the members of the current group, the method iterateCurrentGroup() is used;
030:         * this underpins the current-group() function in XSLT. The grouping key for the
031:         * current group is available via the getCurrentGroupingKey() method.</p>
032:         */
033:
034:        public class GroupByIterator implements  GroupIterator,
035:                LastPositionFinder, LookaheadIterator {
036:
037:            // The implementation of group-by is not pipelined. All the items in the population
038:            // are read at the start, their grouping keys are calculated, and the groups are formed
039:            // in memory as a hash table indexed by the grouping key. This hash table is then
040:            // flattened into three parallel lists: a list of groups (each group being represented
041:            // as a list of items in population order), a list of grouping keys, and a list of
042:            // the initial items of the groups.
043:
044:            private SequenceIterator population;
045:            private Expression keyExpression;
046:            private Comparator collator;
047:            private XPathContext keyContext;
048:            private int position = 0;
049:
050:            // Main data structure holds one entry for each group. The entry is also an ArrayList,
051:            // which contains the Items that are members of the group, in population order.
052:            // The groups are arranged in order of first appearance within the population.
053:            private ArrayList groups = new ArrayList(40);
054:
055:            // This parallel structure identifies the grouping key for each group. The list
056:            // corresponds one-to-one with the list of groups.
057:            private ArrayList groupKeys = new ArrayList(40);
058:
059:            // For convenience (so that we can use a standard ArrayListIterator) we define
060:            // another parallel array holding the initial items of each group.
061:            private ArrayList initialItems = new ArrayList(40);
062:
063:            // An AtomicSortComparer is used to do the comparisons
064:            private AtomicSortComparer comparer;
065:
066:            /**
067:             * Create a GroupByIterator
068:             * @param population iterator over the population to be grouped
069:             * @param keyExpression the expression used to calculate the grouping key
070:             * @param keyContext dynamic context for calculating the grouping key
071:             * @param collator Collation to be used for comparing grouping keys
072:             * @throws XPathException
073:             */
074:
075:            public GroupByIterator(SequenceIterator population,
076:                    Expression keyExpression, XPathContext keyContext,
077:                    Comparator collator) throws XPathException {
078:                this .population = population;
079:                this .keyExpression = keyExpression;
080:                this .keyContext = keyContext;
081:                this .collator = collator;
082:                this .comparer = new AtomicSortComparer(collator, keyContext);
083:                buildIndexedGroups();
084:            }
085:
086:            /**
087:             * Build the grouping table forming groups of items with equal keys.
088:             * This form of grouping allows a member of the population to be present in zero
089:             * or more groups, one for each value of the grouping key.
090:             */
091:
092:            private void buildIndexedGroups() throws XPathException {
093:                HashMap index = new HashMap(40);
094:                XPathContext c2 = keyContext.newMinorContext();
095:                c2.setCurrentIterator(population);
096:                c2.setOriginatingConstructType(Location.GROUPING_KEY);
097:                while (true) {
098:                    Item item = population.next();
099:                    if (item == null) {
100:                        break;
101:                    }
102:                    SequenceIterator keys = keyExpression.iterate(c2);
103:                    boolean firstKey = true;
104:                    while (true) {
105:                        AtomicValue key = (AtomicValue) keys.next();
106:                        if (key == null) {
107:                            break;
108:                        }
109:                        AtomicSortComparer.ComparisonKey comparisonKey = comparer
110:                                .getComparisonKey(key);
111:                        ArrayList g = (ArrayList) index.get(comparisonKey);
112:                        if (g == null) {
113:                            ArrayList newGroup = new ArrayList(20);
114:                            newGroup.add(item);
115:                            groups.add(newGroup);
116:                            groupKeys.add(key);
117:                            initialItems.add(item);
118:                            index.put(comparisonKey, newGroup);
119:                        } else {
120:                            if (firstKey) {
121:                                g.add(item);
122:                            } else {
123:                                // if this is not the first key value for this item, we
124:                                // check whether the item is already in this group before
125:                                // adding it again. If it is in this group, then we know
126:                                // it will be at the end.
127:                                if (g.get(g.size() - 1) != item) {
128:                                    g.add(item);
129:                                }
130:                            }
131:                        }
132:                        firstKey = false;
133:                    }
134:                }
135:            }
136:
137:            /**
138:             * Get the value of the grouping key for the current group
139:             * @return the grouping key
140:             */
141:
142:            public AtomicValue getCurrentGroupingKey() {
143:                return (AtomicValue) groupKeys.get(position - 1);
144:            }
145:
146:            /**
147:             * Get an iterator over the items in the current group
148:             * @return the iterator
149:             */
150:
151:            public SequenceIterator iterateCurrentGroup() {
152:                return new ListIterator((ArrayList) groups.get(position - 1));
153:            }
154:
155:            /**
156:             * Get the contents of the current group as a java List
157:             * @return the contents of the current group
158:             */
159:
160:            public List getCurrentGroup() {
161:                return (ArrayList) groups.get(position - 1);
162:            }
163:
164:            public boolean hasNext() {
165:                return position < groups.size();
166:            }
167:
168:            public Item next() throws XPathException {
169:                if (position < groups.size()) {
170:                    position++;
171:                    return current();
172:                } else {
173:                    position = -1;
174:                    return null;
175:                }
176:            }
177:
178:            public Item current() {
179:                if (position < 1) {
180:                    return null;
181:                }
182:                // return the initial item of the current group
183:                return (Item) ((ArrayList) groups.get(position - 1)).get(0);
184:            }
185:
186:            public int position() {
187:                return position;
188:            }
189:
190:            public SequenceIterator getAnother() throws XPathException {
191:                XPathContext c2 = keyContext.newMinorContext();
192:                c2.setOriginatingConstructType(Location.GROUPING_KEY);
193:                return new GroupByIterator(population.getAnother(),
194:                        keyExpression, c2, collator);
195:            }
196:
197:            /**
198:             * Get properties of this iterator, as a bit-significant integer.
199:             *
200:             * @return the properties of this iterator. This will be some combination of
201:             *         properties such as {@link GROUNDED}, {@link LAST_POSITION_FINDER},
202:             *         and {@link LOOKAHEAD}. It is always
203:             *         acceptable to return the value zero, indicating that there are no known special properties.
204:             *         It is acceptable for the properties of the iterator to change depending on its state.
205:             */
206:
207:            public int getProperties() {
208:                return LAST_POSITION_FINDER | LOOKAHEAD;
209:            }
210:
211:            /**
212:             * Get the last position (that is, the number of groups)
213:             */
214:
215:            public int getLastPosition() throws XPathException {
216:                return groups.size();
217:            }
218:
219:        }
220:
221:        //
222:        // The contents of this file are subject to the Mozilla Public License Version 1.0 (the "License");
223:        // you may not use this file except in compliance with the License. You may obtain a copy of the
224:        // License at http://www.mozilla.org/MPL/
225:        //
226:        // Software distributed under the License is distributed on an "AS IS" basis,
227:        // WITHOUT WARRANTY OF ANY KIND, either express or implied.
228:        // See the License for the specific language governing rights and limitations under the License.
229:        //
230:        // The Original Code is: all this file.
231:        //
232:        // The Initial Developer of the Original Code is Michael H. Kay
233:        //
234:        // Portions created by (your name) are Copyright (C) (your legal entity). All Rights Reserved.
235:        //
236:        // Contributor(s): none
237:        //
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