SimilarItems.java

/**
 * 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.codelibs.elasticsearch.taste.similarity.precompute;

import java.util.List;
import java.util.NoSuchElementException;

import org.codelibs.elasticsearch.taste.recommender.RecommendedItem;

import com.google.common.collect.UnmodifiableIterator;

/**
 * Compact representation of all similar items for an item
 */
public class SimilarItems {

    private final long itemID;

    private final long[] similarItemIDs;

    private final double[] similarities;

    public SimilarItems(final long itemID,
            final List<RecommendedItem> similarItems) {
        this.itemID = itemID;

        final int numSimilarItems = similarItems.size();
        similarItemIDs = new long[numSimilarItems];
        similarities = new double[numSimilarItems];

        for (int n = 0; n < numSimilarItems; n++) {
            similarItemIDs[n] = similarItems.get(n).getItemID();
            similarities[n] = similarItems.get(n).getValue();
        }
    }

    public long getItemID() {
        return itemID;
    }

    public int numSimilarItems() {
        return similarItemIDs.length;
    }

    public Iterable<SimilarItem> getSimilarItems() {
        return () -> new SimilarItemsIterator();
    }

    private class SimilarItemsIterator extends
            UnmodifiableIterator<SimilarItem> {

        private int index = 0;

        @Override
        public boolean hasNext() {
            return index < similarItemIDs.length - 1;
        }

        @Override
        public SimilarItem next() {
            if (!hasNext()) {
                throw new NoSuchElementException();
            }
            index++;
            return new SimilarItem(similarItemIDs[index], similarities[index]);
        }
    }
}