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

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Here is the source code for org.apache.mahout.cf.taste.hadoop.similarity.item.SimilarityReducer.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 java.io.IOException;
import java.util.Iterator;

import org.apache.hadoop.io.DoubleWritable;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapred.MapReduceBase;
import org.apache.hadoop.mapred.OutputCollector;
import org.apache.hadoop.mapred.Reducer;
import org.apache.hadoop.mapred.Reporter;
import org.apache.mahout.cf.taste.hadoop.EntityEntityWritable;
import org.apache.mahout.cf.taste.hadoop.similarity.CoRating;
import org.apache.mahout.cf.taste.hadoop.similarity.DistributedItemSimilarity;

/**
 * Finally compute the similarity for each item-pair, that has been corated at least once.
 * Computation is done with an external implementation of {@link DistributedItemSimilarity}.
 */
public final class SimilarityReducer extends MapReduceBase
        implements Reducer<ItemPairWritable, CoRating, EntityEntityWritable, DoubleWritable> {

    private DistributedItemSimilarity distributedItemSimilarity;
    private int numberOfUsers;

    @Override
    public void configure(JobConf jobConf) {
        super.configure(jobConf);
        distributedItemSimilarity = ItemSimilarityJob
                .instantiateSimilarity(jobConf.get(ItemSimilarityJob.DISTRIBUTED_SIMILARITY_CLASSNAME));
        numberOfUsers = jobConf.getInt(ItemSimilarityJob.NUMBER_OF_USERS, -1);
        if (numberOfUsers <= 0) {
            throw new IllegalStateException("Number of users was not set correctly");
        }
    }

    @Override
    public void reduce(ItemPairWritable pair, Iterator<CoRating> coRatings,
            OutputCollector<EntityEntityWritable, DoubleWritable> output, Reporter reporter) throws IOException {

        double similarity = distributedItemSimilarity.similarity(coRatings, pair.getItemAWeight(),
                pair.getItemBWeight(), numberOfUsers);

        if (!Double.isNaN(similarity)) {
            output.collect(pair.getItemItemWritable(), new DoubleWritable(similarity));
        }
    }

}