org.apache.hadoop.mapreduce.lib.aggregate
Class ValueAggregatorReducer<K1 extends WritableComparable<?>,V1 extends Writable>

java.lang.Object
  extended by org.apache.hadoop.mapreduce.Reducer<Text,Text,Text,Text>
      extended by org.apache.hadoop.mapreduce.lib.aggregate.ValueAggregatorReducer<K1,V1>

@InterfaceAudience.Public
@InterfaceStability.Stable
public class ValueAggregatorReducer<K1 extends WritableComparable<?>,V1 extends Writable>
extends Reducer<Text,Text,Text,Text>

This class implements the generic reducer of Aggregate.


Constructor Summary
ValueAggregatorReducer()
           
 
Method Summary
 void reduce(Text key, Iterable<Text> values, org.apache.hadoop.mapreduce.Reducer.Context context)
          This method is called once for each key.
 void setup(org.apache.hadoop.mapreduce.Reducer.Context context)
          Called once at the start of the task.
 
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

ValueAggregatorReducer

public ValueAggregatorReducer()
Method Detail

setup

public void setup(org.apache.hadoop.mapreduce.Reducer.Context context)
           throws IOException,
                  InterruptedException
Description copied from class: Reducer
Called once at the start of the task.

Overrides:
setup in class Reducer<Text,Text,Text,Text>
Throws:
IOException
InterruptedException

reduce

public void reduce(Text key,
                   Iterable<Text> values,
                   org.apache.hadoop.mapreduce.Reducer.Context context)
            throws IOException,
                   InterruptedException
Description copied from class: Reducer
This method is called once for each key. Most applications will define their reduce class by overriding this method. The default implementation is an identity function.

Overrides:
reduce in class Reducer<Text,Text,Text,Text>
Parameters:
key - the key is expected to be a Text object, whose prefix indicates the type of aggregation to aggregate the values. In effect, data driven computing is achieved. It is assumed that each aggregator's getReport method emits appropriate output for the aggregator. This may be further customized.
values - the values to be aggregated
context -
Throws:
IOException
InterruptedException


Copyright © 2012 Apache Software Foundation. All Rights Reserved.