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package org.apache.lucene.search.grouping;
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership.
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* The ASF licenses this file to You under the Apache License, Version 2.0
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* (the "License"); you may not use this file except in compliance with
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* the License. You may obtain a copy of the License at
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* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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import java.io.IOException;
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import java.util.Collection;
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import java.util.HashMap;
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import org.apache.lucene.index.IndexReader;
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import org.apache.lucene.search.*;
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* SecondPassGroupingCollector is the second of two passes
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* necessary to collect grouped docs. This pass gathers the
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* top N documents per top group computed from the
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* first pass. Concrete subclasses define what a group is and how it
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* is internally collected.
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* <p>See {@link org.apache.lucene.search.grouping} for more
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* details including a full code example.</p>
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* @lucene.experimental
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public abstract class AbstractSecondPassGroupingCollector<GROUP_VALUE_TYPE> extends Collector {
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protected final Map<GROUP_VALUE_TYPE, SearchGroupDocs<GROUP_VALUE_TYPE>> groupMap;
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private final int maxDocsPerGroup;
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protected SearchGroupDocs<GROUP_VALUE_TYPE>[] groupDocs;
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private final Collection<SearchGroup<GROUP_VALUE_TYPE>> groups;
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private final Sort withinGroupSort;
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private final Sort groupSort;
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private int totalHitCount;
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private int totalGroupedHitCount;
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public AbstractSecondPassGroupingCollector(Collection<SearchGroup<GROUP_VALUE_TYPE>> groups, Sort groupSort, Sort withinGroupSort,
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int maxDocsPerGroup, boolean getScores, boolean getMaxScores, boolean fillSortFields)
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//System.out.println("SP init");
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if (groups.size() == 0) {
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throw new IllegalArgumentException("no groups to collect (groups.size() is 0)");
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this.groupSort = groupSort;
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this.withinGroupSort = withinGroupSort;
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this.maxDocsPerGroup = maxDocsPerGroup;
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groupMap = new HashMap<GROUP_VALUE_TYPE, SearchGroupDocs<GROUP_VALUE_TYPE>>(groups.size());
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for (SearchGroup<GROUP_VALUE_TYPE> group : groups) {
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//System.out.println(" prep group=" + (group.groupValue == null ? "null" : group.groupValue.utf8ToString()));
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final TopDocsCollector collector;
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if (withinGroupSort == null) {
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collector = TopScoreDocCollector.create(maxDocsPerGroup, true);
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collector = TopFieldCollector.create(withinGroupSort, maxDocsPerGroup, fillSortFields, getScores, getMaxScores, true);
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groupMap.put(group.groupValue,
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new SearchGroupDocs<GROUP_VALUE_TYPE>(group.groupValue,
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public void setScorer(Scorer scorer) throws IOException {
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for (SearchGroupDocs<GROUP_VALUE_TYPE> group : groupMap.values()) {
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group.collector.setScorer(scorer);
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public void collect(int doc) throws IOException {
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SearchGroupDocs<GROUP_VALUE_TYPE> group = retrieveGroup(doc);
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totalGroupedHitCount++;
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group.collector.collect(doc);
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* Returns the group the specified doc belongs to or <code>null</code> if no group could be retrieved.
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* @param doc The specified doc
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* @return the group the specified doc belongs to or <code>null</code> if no group could be retrieved
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* @throws IOException If an I/O related error occurred
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protected abstract SearchGroupDocs<GROUP_VALUE_TYPE> retrieveGroup(int doc) throws IOException;
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public void setNextReader(IndexReader reader, int docBase) throws IOException {
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//System.out.println("SP.setNextReader");
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for (SearchGroupDocs<GROUP_VALUE_TYPE> group : groupMap.values()) {
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group.collector.setNextReader(reader, docBase);
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public boolean acceptsDocsOutOfOrder() {
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public TopGroups<GROUP_VALUE_TYPE> getTopGroups(int withinGroupOffset) {
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@SuppressWarnings("unchecked")
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final GroupDocs<GROUP_VALUE_TYPE>[] groupDocsResult = (GroupDocs<GROUP_VALUE_TYPE>[]) new GroupDocs[groups.size()];
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for(SearchGroup group : groups) {
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final SearchGroupDocs<GROUP_VALUE_TYPE> groupDocs = groupMap.get(group.groupValue);
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final TopDocs topDocs = groupDocs.collector.topDocs(withinGroupOffset, maxDocsPerGroup);
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groupDocsResult[groupIDX++] = new GroupDocs<GROUP_VALUE_TYPE>(topDocs.getMaxScore(),
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groupDocs.groupValue,
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return new TopGroups<GROUP_VALUE_TYPE>(groupSort.getSort(),
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withinGroupSort == null ? null : withinGroupSort.getSort(),
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totalHitCount, totalGroupedHitCount, groupDocsResult);
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// TODO: merge with SearchGroup or not?
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// ad: don't need to build a new hashmap
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// disad: blows up the size of SearchGroup if we need many of them, and couples implementations
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public class SearchGroupDocs<GROUP_VALUE_TYPE> {
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public final GROUP_VALUE_TYPE groupValue;
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public final TopDocsCollector collector;
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public SearchGroupDocs(GROUP_VALUE_TYPE groupValue, TopDocsCollector collector) {
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this.groupValue = groupValue;
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this.collector = collector;