org.apache.mahout.cf.taste.hadoop.similarity.item.TopSimilarItemsQueue.java Source code

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Here is the source code for org.apache.mahout.cf.taste.hadoop.similarity.item.TopSimilarItemsQueue.java

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/**
 * 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 com.google.common.collect.Lists;
import org.apache.lucene.util.PriorityQueue;
import org.apache.mahout.cf.taste.similarity.precompute.SimilarItem;

import java.util.Collections;
import java.util.List;

public class TopSimilarItemsQueue extends PriorityQueue<SimilarItem> {

    private static final long SENTINEL_ID = Long.MIN_VALUE;

    private final int maxSize;

    public TopSimilarItemsQueue(int maxSize) {
        super(maxSize);
        this.maxSize = maxSize;
    }

    public List<SimilarItem> getTopItems() {
        List<SimilarItem> items = Lists.newArrayListWithCapacity(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);
    }
}