org.hf.mls.mahout.cf.taste.hadoop.preparation.ToItemVectorsMapper.java Source code

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Here is the source code for org.hf.mls.mahout.cf.taste.hadoop.preparation.ToItemVectorsMapper.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.hf.mls.mahout.cf.taste.hadoop.preparation;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.mahout.cf.taste.hadoop.TasteHadoopUtils;
import org.apache.mahout.math.RandomAccessSparseVector;
import org.apache.mahout.math.VarLongWritable;
import org.apache.mahout.math.Vector;
import org.apache.mahout.math.VectorWritable;
import org.apache.mahout.math.hadoop.similarity.cooccurrence.Vectors;

import java.io.IOException;

public class ToItemVectorsMapper extends Mapper<VarLongWritable, VectorWritable, IntWritable, VectorWritable> {

    public static final String SAMPLE_SIZE = ToItemVectorsMapper.class + ".sampleSize";

    enum Elements {
        USER_RATINGS_USED, USER_RATINGS_NEGLECTED
    }

    private final IntWritable itemID = new IntWritable();
    private final VectorWritable itemVectorWritable = new VectorWritable();

    private int sampleSize;

    @Override
    protected void setup(Context ctx) throws IOException, InterruptedException {
        sampleSize = ctx.getConfiguration().getInt(SAMPLE_SIZE, Integer.MAX_VALUE);
    }

    @Override
    protected void map(VarLongWritable rowIndex, VectorWritable vectorWritable, Context ctx)
            throws IOException, InterruptedException {
        Vector userRatings = vectorWritable.get();

        int numElementsBeforeSampling = userRatings.getNumNondefaultElements();
        userRatings = Vectors.maybeSample(userRatings, sampleSize);
        int numElementsAfterSampling = userRatings.getNumNondefaultElements();

        int column = TasteHadoopUtils.idToIndex(rowIndex.get());

        itemVectorWritable.setWritesLaxPrecision(true);

        Vector itemVector = new RandomAccessSparseVector(Integer.MAX_VALUE, 1);
        for (Vector.Element elem : userRatings.nonZeroes()) {
            itemID.set(elem.index());
            itemVector.setQuick(column, elem.get());
            itemVectorWritable.set(itemVector);
            ctx.write(itemID, itemVectorWritable);
            // reset vector for reuse
            itemVector.setQuick(elem.index(), 0.0);
        }

        ctx.getCounter(Elements.USER_RATINGS_USED).increment(numElementsAfterSampling);
        ctx.getCounter(Elements.USER_RATINGS_NEGLECTED)
                .increment(numElementsBeforeSampling - numElementsAfterSampling);
    }

}