/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.lucene.search.grouping;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import org.apache.lucene.search.SimpleCollector;
/**
* A second pass grouping collector that keeps track of distinct values for a specified field for the top N group.
*
* @lucene.experimental
*/
public abstract class AbstractDistinctValuesCollector<GC extends AbstractDistinctValuesCollector.GroupCount<?>> extends SimpleCollector {
/**
* Returns all unique values for each top N group.
*
* @return all unique values for each top N group
*/
public abstract List<GC> getGroups();
/**
* Returned by {@link AbstractDistinctValuesCollector#getGroups()},
* representing the value and set of distinct values for the group.
*/
public abstract static class GroupCount<GROUP_VALUE_TYPE> {
public final GROUP_VALUE_TYPE groupValue;
public final Set<GROUP_VALUE_TYPE> uniqueValues;
public GroupCount(GROUP_VALUE_TYPE groupValue) {
this.groupValue = groupValue;
this.uniqueValues = new HashSet<>();
}
}
@Override
public boolean needsScores() {
return false; // not needed to fetch all values
}
}