Package org.apache.hadoop.mapreduce.lib.aggregate

Class ValueAggregatorReducer<K1 extends WritableComparable<?>,V1 extends Writable>

java.lang.Object

org.apache.hadoop.mapreduce.Reducer<Text,Text,Text,Text>

org.apache.hadoop.mapreduce.lib.aggregate.ValueAggregatorReducer<K1,V1>

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

This class implements the generic reducer of Aggregate.

Nested Class Summary

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

org.apache.hadoop.mapreduce.Reducer.Context

Constructor Summary

Constructors

Constructor	Description
ValueAggregatorReducer()

Method Summary

Modifier and Type	Method	Description
void	reduce(Text key, Iterable<Text> values, Reducer<Text,Text,Text,Text>.org.apache.hadoop.mapreduce.Reducer.Context context)	This method is called once for each key.
void	setup(Reducer<Text,Text,Text,Text>.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 Details

ValueAggregatorReducer

public ValueAggregatorReducer()

Method Details

setup

public void setup(Reducer<Text,Text,Text,Text>.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,
 Reducer<Text,Text,Text,Text>.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