org.apache.crunch.lib

Class Aggregate.TopKFn<K,V>

java.lang.Object

org.apache.crunch.DoFn<Pair<K,V>,Pair<Integer,Pair<K,V>>>

org.apache.crunch.lib.Aggregate.TopKFn<K,V>

All Implemented Interfaces:

Serializable

Enclosing class:

Aggregate

public static class Aggregate.TopKFn<K,V>
extends DoFn<Pair<K,V>,Pair<Integer,Pair<K,V>>>

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
Aggregate.TopKFn(int limit, boolean ascending)

Method Summary

Methods

Modifier and Type	Method and Description
void	cleanup(Emitter<Pair<Integer,Pair<K,V>>> emitter) Called during the cleanup of the MapReduce job this DoFn is associated with.
void	initialize() Initialize this DoFn.
void	process(Pair<K,V> input, Emitter<Pair<Integer,Pair<K,V>>> emitter) Processes the records from a PCollection.

Methods inherited from class org.apache.crunch.DoFn

configure, scaleFactor, setContext

Methods inherited from class java.lang.Object

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

Constructor Detail

Aggregate.TopKFn

public Aggregate.TopKFn(int limit,
                boolean ascending)

Method Detail

initialize

public void initialize()

Description copied from class: DoFn

Initialize this DoFn. This initialization will happen before the actual DoFn.process(Object, Emitter) is triggered. Subclasses may override this method to do appropriate initialization.

Called during the setup of the job instance this DoFn is associated with.

Overrides:

initialize in class DoFn<Pair<K,V>,Pair<Integer,Pair<K,V>>>

process

public void process(Pair<K,V> input,
           Emitter<Pair<Integer,Pair<K,V>>> emitter)

Description copied from class: DoFn

Processes the records from a PCollection.

Note: Crunch can reuse a single input record object whose content changes on each DoFn.process(Object, Emitter) method call. This functionality is imposed by Hadoop's Reducer implementation: The framework will reuse the key and value objects that are passed into the reduce, therefore the application should clone the objects they want to keep a copy of.

Specified by:

process in class DoFn<Pair<K,V>,Pair<Integer,Pair<K,V>>>

Parameters:

input - The input record.

emitter - The emitter to send the output to

cleanup

public void cleanup(Emitter<Pair<Integer,Pair<K,V>>> emitter)

Description copied from class: DoFn

Called during the cleanup of the MapReduce job this DoFn is associated with. Subclasses may override this method to do appropriate cleanup.

Overrides:

cleanup in class DoFn<Pair<K,V>,Pair<Integer,Pair<K,V>>>

Parameters:

emitter - The emitter that was used for output