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

java.lang.Object
  extended by org.apache.hadoop.mapreduce.Reducer<VarLongWritable,PrefAndSimilarityColumnWritable,VarLongWritable,RecommendedItemsWritable>
      extended by 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
AggregateAndRecommendReducer()
           
 
Method Summary
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


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