com.google.appengine.tools.mapreduce.reducers

Class KeyProjectionReducer<K,V>

java.lang.Object

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

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

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

Type Parameters:

K - type of keys

V - type of values (discarded)

All Implemented Interfaces:

Serializable

public class KeyProjectionReducer<K,V>
extends Reducer<K,V,K>

Reducer that emits the keys that occur in its input, discarding the values.

Author:

ohler@google.com (Christian Ohler)

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
KeyProjectionReducer()

Method Summary

Methods

Modifier and Type	Method and Description
static <K,V> KeyProjectionReducer<K,V>	create()
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

KeyProjectionReducer

public KeyProjectionReducer()

Method Detail

create

public static <K,V> KeyProjectionReducer<K,V> create()

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,K>