org.apache.mahout.cf.taste.hadoop.item

Class AggregateAndRecommendReducer

java.lang.Object

org.apache.hadoop.mapreduce.Reducer<VarLongWritable,PrefAndSimilarityColumnWritable,VarLongWritable,RecommendedItemsWritable>

org.apache.mahout.cf.taste.hadoop.item.AggregateAndRecommendReducer

public final class AggregateAndRecommendReducer
extends org.apache.hadoop.mapreduce.Reducer<VarLongWritable,PrefAndSimilarityColumnWritable,VarLongWritable,RecommendedItemsWritable>

computes prediction values for each user

 u = a user
 i = an item not yet rated by u
 N = all items similar to i (where similarity is usually computed by pairwisely comparing the item-vectors
 of the user-item matrix)

 Prediction(u,i) = sum(all n from N: similarity(i,n) * rating(u,n)) / sum(all n from N: abs(similarity(i,n)))
 

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.hadoop.mapreduce.Reducer

org.apache.hadoop.mapreduce.Reducer.Context

Constructor Summary

Constructors

Constructor and Description
AggregateAndRecommendReducer()

Method Summary

Modifier and Type	Method and Description
protected void	reduce(VarLongWritable userID, Iterable<PrefAndSimilarityColumnWritable> values, org.apache.hadoop.mapreduce.Reducer.Context context)
protected void	setup(org.apache.hadoop.mapreduce.Reducer.Context context)

Methods inherited from class org.apache.hadoop.mapreduce.Reducer

cleanup, run

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

AggregateAndRecommendReducer

public AggregateAndRecommendReducer()

Method Detail

setup

protected void setup(org.apache.hadoop.mapreduce.Reducer.Context context)
              throws IOException

Overrides:

setup in class org.apache.hadoop.mapreduce.Reducer<VarLongWritable,PrefAndSimilarityColumnWritable,VarLongWritable,RecommendedItemsWritable>

Throws:

IOException

reduce

protected void reduce(VarLongWritable userID,
                      Iterable<PrefAndSimilarityColumnWritable> values,
                      org.apache.hadoop.mapreduce.Reducer.Context context)
               throws IOException,
                      InterruptedException

Overrides:

reduce in class org.apache.hadoop.mapreduce.Reducer<VarLongWritable,PrefAndSimilarityColumnWritable,VarLongWritable,RecommendedItemsWritable>

Throws:

IOException

InterruptedException