org.apache.mahout.cf.taste.hadoop.item.UserVectorSplitterMapper.java Source code

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Here is the source code for org.apache.mahout.cf.taste.hadoop.item.UserVectorSplitterMapper.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.item;

import com.google.common.io.Closeables;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.mahout.cf.taste.common.TopK;
import org.apache.mahout.cf.taste.impl.common.FastIDSet;
import org.apache.mahout.common.iterator.FileLineIterable;
import org.apache.mahout.math.VarIntWritable;
import org.apache.mahout.math.VarLongWritable;
import org.apache.mahout.math.Vector;
import org.apache.mahout.math.VectorWritable;

import java.io.IOException;
import java.util.Comparator;
import java.util.Iterator;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public final class UserVectorSplitterMapper
        extends Mapper<VarLongWritable, VectorWritable, VarIntWritable, VectorOrPrefWritable> {

    private static final Logger log = LoggerFactory.getLogger(UserVectorSplitterMapper.class);

    static final String USERS_FILE = "usersFile";
    static final String MAX_PREFS_PER_USER_CONSIDERED = "maxPrefsPerUserConsidered";
    static final int DEFAULT_MAX_PREFS_PER_USER_CONSIDERED = 10;

    private int maxPrefsPerUserConsidered;
    private FastIDSet usersToRecommendFor;

    @Override
    protected void setup(Context context) throws IOException {
        Configuration jobConf = context.getConfiguration();
        maxPrefsPerUserConsidered = jobConf.getInt(MAX_PREFS_PER_USER_CONSIDERED,
                DEFAULT_MAX_PREFS_PER_USER_CONSIDERED);
        String usersFilePathString = jobConf.get(USERS_FILE);
        if (usersFilePathString != null) {
            FSDataInputStream in = null;
            try {
                Path unqualifiedUsersFilePath = new Path(usersFilePathString);
                FileSystem fs = FileSystem.get(unqualifiedUsersFilePath.toUri(), jobConf);
                usersToRecommendFor = new FastIDSet();
                Path usersFilePath = unqualifiedUsersFilePath.makeQualified(fs);
                in = fs.open(usersFilePath);
                for (String line : new FileLineIterable(in)) {
                    try {
                        usersToRecommendFor.add(Long.parseLong(line));
                    } catch (NumberFormatException nfe) {
                        log.warn("usersFile line ignored: {}", line);
                    }
                }
            } finally {
                Closeables.closeQuietly(in);
            }
        }
    }

    @Override
    protected void map(VarLongWritable key, VectorWritable value, Context context)
            throws IOException, InterruptedException {
        long userID = key.get();
        if (usersToRecommendFor != null && !usersToRecommendFor.contains(userID)) {
            return;
        }
        Vector userVector = maybePruneUserVector(value.get());
        Iterator<Vector.Element> it = userVector.iterateNonZero();
        VarIntWritable itemIndexWritable = new VarIntWritable();
        VectorOrPrefWritable vectorOrPref = new VectorOrPrefWritable();
        while (it.hasNext()) {
            Vector.Element e = it.next();
            itemIndexWritable.set(e.index());
            vectorOrPref.set(userID, (float) e.get());
            context.write(itemIndexWritable, vectorOrPref);
        }
    }

    private Vector maybePruneUserVector(Vector userVector) {
        if (userVector.getNumNondefaultElements() <= maxPrefsPerUserConsidered) {
            return userVector;
        }

        float smallestLargeValue = findSmallestLargeValue(userVector);

        // "Blank out" small-sized prefs to reduce the amount of partial products
        // generated later. They're not zeroed, but NaN-ed, so they come through
        // and can be used to exclude these items from prefs.
        Iterator<Vector.Element> it = userVector.iterateNonZero();
        while (it.hasNext()) {
            Vector.Element e = it.next();
            float absValue = Math.abs((float) e.get());
            if (absValue < smallestLargeValue) {
                e.set(Float.NaN);
            }
        }

        return userVector;
    }

    private float findSmallestLargeValue(Vector userVector) {

        TopK<Float> topPrefValues = new TopK<Float>(maxPrefsPerUserConsidered, new Comparator<Float>() {
            @Override
            public int compare(Float one, Float two) {
                return one.compareTo(two);
            }
        });

        Iterator<Vector.Element> it = userVector.iterateNonZero();
        while (it.hasNext()) {
            float absValue = Math.abs((float) it.next().get());
            topPrefValues.offer(absValue);
        }
        return topPrefValues.smallestGreat();
    }

}