com.google.appengine.tools.mapreduce.reducers

Class IdentityReducer<K,V>

java.lang.Object

com.google.appengine.tools.mapreduce.Worker<ReducerContext<O>>

com.google.appengine.tools.mapreduce.Reducer<K,V,KeyValue<K,List<V>>>

com.google.appengine.tools.mapreduce.reducers.IdentityReducer<K,V>

Type Parameters:

K - the type of the key

V - the type of the value

All Implemented Interfaces:

Serializable

public class IdentityReducer<K,V>
extends Reducer<K,V,KeyValue<K,List<V>>>

A passthrough reducer that passes it's input to it's output.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
IdentityReducer(int maxGroupedValues)

Method Summary

Methods

Modifier and Type	Method and Description
void	reduce(K key, ReducerInput<V> values) Processes the values for a given key, using the context returned by Worker.getContext() to emit output to the Output of the MapReduce.

Methods inherited from class com.google.appengine.tools.mapreduce.Reducer

emit

Methods inherited from class com.google.appengine.tools.mapreduce.Worker

allowSliceRetry, beginShard, beginSlice, endShard, endSlice, estimateMemoryRequirement, getContext, setContext

Methods inherited from class java.lang.Object

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

Constructor Detail

IdentityReducer

public IdentityReducer(int maxGroupedValues)

Parameters:

maxGroupedValues - The number of consecutive values that will be grouped together in a single emit call. If there are more than this number of values emit will be called multiple times with the same key.

Method Detail

reduce

public void reduce(K key,
          ReducerInput<V> values)

Description copied from class: Reducer

Processes the values for a given key, using the context returned by Worker.getContext() to emit output to the Output of the MapReduce. values enumerates all values that the map phase produced for the key key. It will always contain at least one value.

Specified by:

reduce in class Reducer<K,V,KeyValue<K,List<V>>>