/*
* 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 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.io.IOUtils;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.mahout.cf.taste.hadoop.RecommendedItemsWritable;
import org.apache.mahout.cf.taste.hadoop.TasteHadoopUtils;
import org.apache.mahout.cf.taste.impl.common.FastIDSet;
import org.apache.mahout.cf.taste.impl.recommender.ByValueRecommendedItemComparator;
import org.apache.mahout.cf.taste.impl.recommender.GenericRecommendedItem;
import org.apache.mahout.cf.taste.recommender.RecommendedItem;
import org.apache.mahout.common.iterator.FileLineIterable;
import org.apache.mahout.math.RandomAccessSparseVector;
import org.apache.mahout.math.VarLongWritable;
import org.apache.mahout.math.Vector;
import org.apache.mahout.math.function.DoubleFunction;
import org.apache.mahout.math.map.OpenIntLongHashMap;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.PriorityQueue;
import java.util.Queue;
/**
* <p>computes prediction values for each user</p>
*
* <pre>
* u = a user
* i = an item not yet rated by u
* N = all items similar to i (where similarity is usually computed by pairwisely comparing the item-vectors
* of the user-item matrix)
*
* Prediction(u,i) = sum(all n from N: similarity(i,n) * rating(u,n)) / sum(all n from N: abs(similarity(i,n)))
* </pre>
*/
public final class AggregateAndRecommendReducer extends
Reducer<VarLongWritable,PrefAndSimilarityColumnWritable,VarLongWritable,RecommendedItemsWritable> {
static final String ITEMID_INDEX_PATH = "itemIDIndexPath";
static final String NUM_RECOMMENDATIONS = "numRecommendations";
static final int DEFAULT_NUM_RECOMMENDATIONS = 10;
static final String ITEMS_FILE = "itemsFile";
private boolean booleanData;
private int recommendationsPerUser;
private FastIDSet itemsToRecommendFor;
private OpenIntLongHashMap indexItemIDMap;
private static final float BOOLEAN_PREF_VALUE = 1.0f;
@Override
protected void setup(Context context) throws IOException {
Configuration jobConf = context.getConfiguration();
recommendationsPerUser = jobConf.getInt(NUM_RECOMMENDATIONS, DEFAULT_NUM_RECOMMENDATIONS);
booleanData = jobConf.getBoolean(RecommenderJob.BOOLEAN_DATA, false);
indexItemIDMap = TasteHadoopUtils.readItemIDIndexMap(jobConf.get(ITEMID_INDEX_PATH), jobConf);
FSDataInputStream in = null;
try {
String itemFilePathString = jobConf.get(ITEMS_FILE);
if (itemFilePathString == null) {
itemsToRecommendFor = null;
} else {
Path unqualifiedItemsFilePath = new Path(itemFilePathString);
FileSystem fs = FileSystem.get(unqualifiedItemsFilePath.toUri(), jobConf);
itemsToRecommendFor = new FastIDSet();
Path itemsFilePath = unqualifiedItemsFilePath.makeQualified(fs);
in = fs.open(itemsFilePath);
for (String line : new FileLineIterable(in)) {
itemsToRecommendFor.add(Long.parseLong(line));
}
}
} finally {
IOUtils.closeStream(in);
}
}
private static final DoubleFunction ABSOLUTE_VALUES = new DoubleFunction() {
@Override
public double apply(double value) {
return value < 0 ? value * -1 : value;
}
};
@Override
protected void reduce(VarLongWritable userID,
Iterable<PrefAndSimilarityColumnWritable> values,
Context context) throws IOException, InterruptedException {
if (booleanData) {
reduceBooleanData(userID, values, context);
} else {
reduceNonBooleanData(userID, values, context);
}
}
private void reduceBooleanData(VarLongWritable userID,
Iterable<PrefAndSimilarityColumnWritable> values,
Context context) throws IOException, InterruptedException {
/* having boolean data, each estimated preference can only be 1,
* however we can't use this to rank the recommended items,
* so we use the sum of similarities for that. */
Vector predictionVector = null;
for (PrefAndSimilarityColumnWritable prefAndSimilarityColumn : values) {
predictionVector = predictionVector == null
? prefAndSimilarityColumn.getSimilarityColumn()
: predictionVector.plus(prefAndSimilarityColumn.getSimilarityColumn());
}
writeRecommendedItems(userID, predictionVector, context);
}
private void reduceNonBooleanData(VarLongWritable userID,
Iterable<PrefAndSimilarityColumnWritable> values,
Context context) throws IOException, InterruptedException {
/* each entry here is the sum in the numerator of the prediction formula */
Vector numerators = null;
/* each entry here is the sum in the denominator of the prediction formula */
Vector denominators = null;
/* each entry here is the number of similar items used in the prediction formula */
Vector numberOfSimilarItemsUsed = new RandomAccessSparseVector(Integer.MAX_VALUE, 100);
for (PrefAndSimilarityColumnWritable prefAndSimilarityColumn : values) {
Vector simColumn = prefAndSimilarityColumn.getSimilarityColumn();
float prefValue = prefAndSimilarityColumn.getPrefValue();
/* count the number of items used for each prediction */
Iterator<Vector.Element> usedItemsIterator = simColumn.iterateNonZero();
while (usedItemsIterator.hasNext()) {
int itemIDIndex = usedItemsIterator.next().index();
numberOfSimilarItemsUsed.setQuick(itemIDIndex, numberOfSimilarItemsUsed.getQuick(itemIDIndex) + 1);
}
numerators = numerators == null
? prefValue == BOOLEAN_PREF_VALUE ? simColumn.clone() : simColumn.times(prefValue)
: numerators.plus(prefValue == BOOLEAN_PREF_VALUE ? simColumn : simColumn.times(prefValue));
simColumn.assign(ABSOLUTE_VALUES);
denominators = denominators == null ? simColumn : denominators.plus(simColumn);
}
if (numerators == null) {
return;
}
Vector recommendationVector = new RandomAccessSparseVector(Integer.MAX_VALUE, 100);
Iterator<Vector.Element> iterator = numerators.iterateNonZero();
while (iterator.hasNext()) {
Vector.Element element = iterator.next();
int itemIDIndex = element.index();
/* preference estimations must be based on at least 2 datapoints */
if (numberOfSimilarItemsUsed.getQuick(itemIDIndex) > 1) {
/* compute normalized prediction */
double prediction = element.get() / denominators.getQuick(itemIDIndex);
recommendationVector.setQuick(itemIDIndex, prediction);
}
}
writeRecommendedItems(userID, recommendationVector, context);
}
/**
* find the top entries in recommendationVector, map them to the real itemIDs and write back the result
*/
private void writeRecommendedItems(VarLongWritable userID, Vector recommendationVector, Context context)
throws IOException, InterruptedException {
Queue<RecommendedItem> topItems =
new PriorityQueue<RecommendedItem>(recommendationsPerUser + 1,
Collections.reverseOrder(ByValueRecommendedItemComparator.getInstance()));
Iterator<Vector.Element> recommendationVectorIterator = recommendationVector.iterateNonZero();
while (recommendationVectorIterator.hasNext()) {
Vector.Element element = recommendationVectorIterator.next();
int index = element.index();
long itemID = indexItemIDMap.get(index);
if (itemsToRecommendFor == null || itemsToRecommendFor.contains(itemID)) {
float value = (float) element.get();
if (!Float.isNaN(value)) {
if (topItems.size() < recommendationsPerUser) {
topItems.add(new GenericRecommendedItem(itemID, value));
} else if (value > topItems.peek().getValue()) {
topItems.add(new GenericRecommendedItem(itemID, value));
topItems.poll();
}
}
}
}
if (!topItems.isEmpty()) {
List<RecommendedItem> recommendations = new ArrayList<RecommendedItem>(topItems.size());
recommendations.addAll(topItems);
Collections.sort(recommendations, ByValueRecommendedItemComparator.getInstance());
context.write(userID, new RecommendedItemsWritable(recommendations));
}
}
}