/*
* 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.slopeone;
import java.io.IOException;
import java.util.Collections;
import java.util.List;
import com.google.common.collect.Lists;
import org.apache.hadoop.io.FloatWritable;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.mahout.cf.taste.hadoop.EntityEntityWritable;
import org.apache.mahout.cf.taste.hadoop.EntityPrefWritable;
import org.apache.mahout.math.VarLongWritable;
public final class SlopeOnePrefsToDiffsReducer extends
Reducer<VarLongWritable,EntityPrefWritable,EntityEntityWritable,FloatWritable> {
@Override
protected void reduce(VarLongWritable key,
Iterable<EntityPrefWritable> values,
Context context) throws IOException, InterruptedException {
List<EntityPrefWritable> prefs = Lists.newArrayList();
for (EntityPrefWritable writable : values) {
prefs.add(new EntityPrefWritable(writable));
}
Collections.sort(prefs, ByItemIDComparator.getInstance());
int size = prefs.size();
for (int i = 0; i < size; i++) {
EntityPrefWritable first = prefs.get(i);
long itemAID = first.getID();
float itemAValue = first.getPrefValue();
for (int j = i + 1; j < size; j++) {
EntityPrefWritable second = prefs.get(j);
long itemBID = second.getID();
float itemBValue = second.getPrefValue();
context.write(new EntityEntityWritable(itemAID, itemBID), new FloatWritable(itemBValue - itemAValue));
}
}
}
}