org.apache.hadoop.mapreduce.lib.aggregate

Class ValueAggregatorReducer<K1 extends org.apache.hadoop.io.WritableComparable<?>,V1 extends org.apache.hadoop.io.Writable>

java.lang.Object

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

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

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

This class implements the generic reducer of Aggregate.

Nested Class Summary

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

Reducer.Context

Constructor Summary

Constructors

Constructor and Description
ValueAggregatorReducer()

Method Summary

Methods

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

Description copied from class: Reducer

Called once at the start of the task.

Overrides:

setup in class Reducer<org.apache.hadoop.io.Text,org.apache.hadoop.io.Text,org.apache.hadoop.io.Text,org.apache.hadoop.io.Text>

Throws:

IOException

InterruptedException

reduce

public void reduce(org.apache.hadoop.io.Text key,
          Iterable<org.apache.hadoop.io.Text> values,
          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<org.apache.hadoop.io.Text,org.apache.hadoop.io.Text,org.apache.hadoop.io.Text,org.apache.hadoop.io.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