/*
* Source code for Listing 6.7
*
* This is simplified version of org.apache.mahout.cf.taste.hadoop.item.PartialMultiplyMapper class
*/
package mia.recommender.ch06;
import java.io.IOException;
import java.util.List;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.mahout.cf.taste.hadoop.item.VectorAndPrefsWritable;
import org.apache.mahout.math.VarLongWritable;
import org.apache.mahout.math.Vector;
import org.apache.mahout.math.VectorWritable;
public class PartialMultiplyMapper
extends
Mapper<IntWritable, VectorAndPrefsWritable, VarLongWritable, VectorWritable> {
public void map(IntWritable key,
VectorAndPrefsWritable vectorAndPrefsWritable, Context context)
throws IOException, InterruptedException {
Vector cooccurrenceColumn = vectorAndPrefsWritable.getVector();
List<Long> userIDs = vectorAndPrefsWritable.getUserIDs();
List<Float> prefValues = vectorAndPrefsWritable.getValues();
for (int i = 0; i < userIDs.size(); i++) {
long userID = userIDs.get(i);
float prefValue = prefValues.get(i);
Vector partialProduct = cooccurrenceColumn.times(prefValue);
context.write(new VarLongWritable(userID),
new VectorWritable(partialProduct));
}
}
}