org.apache.mahout.cf.taste.hadoop.similarity.item.TopSimilarItemsQueue Maven / Gradle / Ivy
/**
* 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.mahout.cf.taste.hadoop.similarity.item;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import org.apache.lucene.util.PriorityQueue;
import org.apache.mahout.cf.taste.similarity.precompute.SimilarItem;
public class TopSimilarItemsQueue extends PriorityQueue {
private static final long SENTINEL_ID = Long.MIN_VALUE;
private final int maxSize;
public TopSimilarItemsQueue(int maxSize) {
super(maxSize);
this.maxSize = maxSize;
}
public List getTopItems() {
List items = new ArrayList<>(maxSize);
while (size() > 0) {
SimilarItem topItem = pop();
// filter out "sentinel" objects necessary for maintaining an efficient priority queue
if (topItem.getItemID() != SENTINEL_ID) {
items.add(topItem);
}
}
Collections.reverse(items);
return items;
}
@Override
protected boolean lessThan(SimilarItem one, SimilarItem two) {
return one.getSimilarity() < two.getSimilarity();
}
@Override
protected SimilarItem getSentinelObject() {
return new SimilarItem(SENTINEL_ID, Double.MIN_VALUE);
}
}