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CombineFn (Apache Crunch 0.9.0 API)

Class CombineFn<S,T>

  extended by org.apache.crunch.DoFn<Pair<S,Iterable<T>>,Pair<S,T>>
      extended by org.apache.crunch.CombineFn<S,T>
All Implemented Interfaces:
Direct Known Subclasses:

public abstract class CombineFn<S,T>
extends DoFn<Pair<S,Iterable<T>>,Pair<S,T>>

A special DoFn implementation that converts an Iterable of values into a single value. If a CombineFn instance is used on a PGroupedTable, the function will be applied to the output of the map stage before the data is passed to the reducer, which can improve the runtime of certain classes of jobs.

Note that the incoming Iterable can only be used to create an Iterator once. Calling Iterable.iterator() method a second time will throw an IllegalStateException.

See Also:
Serialized Form

Constructor Summary
Method Summary
Methods inherited from class org.apache.crunch.DoFn
cleanup, configure, disableDeepCopy, getConfiguration, getContext, getCounter, getCounter, getStatus, getTaskAttemptID, increment, increment, increment, increment, initialize, process, progress, scaleFactor, setConfiguration, setContext, setStatus
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail


public CombineFn()

Copyright © 2014 The Apache Software Foundation. All Rights Reserved.