org.apache.mahout.cf.taste.hadoop.preparation.ToItemVectorsMapper Maven / Gradle / Ivy
/**
* 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.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 java.io.IOException;
public class ToItemVectorsMapper
extends Mapper {
private final IntWritable itemID = new IntWritable();
private final VectorWritable itemVectorWritable = new VectorWritable();
@Override
protected void map(VarLongWritable rowIndex, VectorWritable vectorWritable, Context ctx)
throws IOException, InterruptedException {
Vector userRatings = vectorWritable.get();
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);
}
}
}