/*
* 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 java.io.IOException;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.mahout.cf.taste.hadoop.EntityPrefWritable;
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;
/**
* <h1>Input</h1>
*
* <p>
* Takes user IDs as {@link VarLongWritable} mapped to all associated item IDs and preference values, as
* {@link EntityPrefWritable}s.
* </p>
*
* <h1>Output</h1>
*
* <p>
* The same user ID mapped to a {@link RandomAccessSparseVector} representation of the same item IDs and
* preference values. Item IDs are used as vector indexes; they are hashed into ints to work as indexes with
* {@link TasteHadoopUtils#idToIndex(long)}. The mapping is remembered for later with a combination of
* {@link ItemIDIndexMapper} and {@link ItemIDIndexReducer}.
* </p>
*/
public final class ToUserVectorsReducer extends
Reducer<VarLongWritable,VarLongWritable,VarLongWritable,VectorWritable> {
public static final String MIN_PREFERENCES_PER_USER = ToUserVectorsReducer.class.getName() +
".minPreferencesPerUser";
private int minPreferences;
public enum Counters { USERS }
@Override
protected void setup(Context ctx) throws IOException, InterruptedException {
super.setup(ctx);
minPreferences = ctx.getConfiguration().getInt(MIN_PREFERENCES_PER_USER, 1);
}
@Override
protected void reduce(VarLongWritable userID,
Iterable<VarLongWritable> itemPrefs,
Context context) throws IOException, InterruptedException {
Vector userVector = new RandomAccessSparseVector(Integer.MAX_VALUE, 100);
for (VarLongWritable itemPref : itemPrefs) {
int index = TasteHadoopUtils.idToIndex(itemPref.get());
float value = itemPref instanceof EntityPrefWritable ? ((EntityPrefWritable) itemPref).getPrefValue() : 1.0f;
userVector.set(index, value);
}
if (userVector.getNumNondefaultElements() >= minPreferences) {
VectorWritable vw = new VectorWritable(userVector);
vw.setWritesLaxPrecision(true);
context.getCounter(Counters.USERS).increment(1);
context.write(userID, vw);
}
}
}