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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 org.apache.lucene.index.IndexReader;
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import org.apache.lucene.search.FieldCache;
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import org.apache.lucene.search.Sort;
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* Concrete implementation of {@link AbstractFirstPassGroupingCollector} that groups based on
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* field values and more specifically uses {@link org.apache.lucene.search.FieldCache.StringIndex}
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* @lucene.experimental
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public class TermFirstPassGroupingCollector extends AbstractFirstPassGroupingCollector<String> {
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private FieldCache.StringIndex index;
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private String groupField;
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* Create the first pass collector.
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* @param groupField The field used to group
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* documents. This field must be single-valued and
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* indexed (FieldCache is used to access its value
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* @param groupSort The {@link Sort} used to sort the
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* groups. The top sorted document within each group
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* according to groupSort, determines how that group
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* sorts against other groups. This must be non-null,
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* ie, if you want to groupSort by relevance use
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* @param topNGroups How many top groups to keep.
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* @throws IOException When I/O related errors occur
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public TermFirstPassGroupingCollector(String groupField, Sort groupSort, int topNGroups) throws IOException {
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super(groupSort, topNGroups);
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this.groupField = groupField;
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protected String getDocGroupValue(int doc) {
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final int ord = index.order[doc];
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return ord == 0 ? null : index.lookup[ord];
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protected String copyDocGroupValue(String groupValue, String reuse) {
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public void setNextReader(IndexReader reader, int docBase) throws IOException {
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super.setNextReader(reader, docBase);
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index = FieldCache.DEFAULT.getStringIndex(reader, groupField);