Java tutorial
/* * 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.gpfvic.mahout.cf.taste.hadoop.item; import java.io.IOException; import org.apache.hadoop.io.IntWritable; import org.apache.hadoop.mapreduce.Mapper; import org.apache.mahout.math.VarIntWritable; import org.apache.mahout.math.Vector; import org.apache.mahout.math.VectorWritable; /** * maps a row of the similarity matrix to a {@link VectorOrPrefWritable} * * actually a column from that matrix has to be used but as the similarity matrix is symmetric, * we can use a row instead of having to transpose it */ public final class SimilarityMatrixRowWrapperMapper extends Mapper<IntWritable, VectorWritable, VarIntWritable, VectorOrPrefWritable> { private final VarIntWritable index = new VarIntWritable(); private final VectorOrPrefWritable vectorOrPref = new VectorOrPrefWritable(); @Override protected void map(IntWritable key, VectorWritable value, Context context) throws IOException, InterruptedException { Vector similarityMatrixRow = value.get(); /* remove self similarity */ similarityMatrixRow.set(key.get(), Double.NaN); index.set(key.get()); vectorOrPref.set(similarityMatrixRow); context.write(index, vectorOrPref); } }