cascading.operation.buffer

Class FirstNBuffer

java.lang.Object

cascading.operation.BaseOperation

cascading.operation.buffer.FirstNBuffer

All Implemented Interfaces:

DeclaresResults, Buffer, Operation, Traceable, Serializable

public class FirstNBuffer
extends BaseOperation
implements Buffer

Class FirstNBuffer will return the first N tuples seen in a given grouping. After the tuples are returned the Buffer stops iterating the arguments unlike the First Aggregator which by contract sees all the values in the grouping.

By default it returns one Tuple.

Order can be controlled through the prior GroupBy or CoGroup pipes.

This class is used by Unique.

See Also:

Serialized Form

Field Summary

Fields inherited from class cascading.operation.BaseOperation

fieldDeclaration, numArgs, trace

Fields inherited from interface cascading.operation.Operation

ANY

Constructor Summary

Constructors

Constructor and Description
FirstNBuffer() Selects and returns the first argument Tuple encountered.
FirstNBuffer(Fields fieldDeclaration) Selects and returns the first argument Tuple encountered.
FirstNBuffer(Fields fieldDeclaration, int firstN) Selects and returns the first N argument Tuples encountered.
FirstNBuffer(int firstN) Selects and returns the first N argument Tuples encountered.

Method Summary

Methods

Modifier and Type	Method and Description
int	getFirstN()
void	operate(FlowProcess flowProcess, BufferCall bufferCall) Method operate is called once for each grouping.

Methods inherited from class cascading.operation.BaseOperation

cleanup, equals, flush, getFieldDeclaration, getNumArgs, getTrace, hashCode, isSafe, prepare, printOperationInternal, toString, toStringInternal

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface cascading.operation.Operation

cleanup, flush, getFieldDeclaration, getNumArgs, isSafe, prepare

Constructor Detail

FirstNBuffer

public FirstNBuffer()

Selects and returns the first argument Tuple encountered.

FirstNBuffer

@ConstructorProperties(value="firstN")
public FirstNBuffer(int firstN)

Selects and returns the first N argument Tuples encountered.

Parameters:

firstN - of type int

FirstNBuffer

@ConstructorProperties(value="fieldDeclaration")
public FirstNBuffer(Fields fieldDeclaration)

Selects and returns the first argument Tuple encountered.

Parameters:

fieldDeclaration - of type Fields

FirstNBuffer

@ConstructorProperties(value={"fieldDeclaration","firstN"})
public FirstNBuffer(Fields fieldDeclaration,
                                       int firstN)

Selects and returns the first N argument Tuples encountered.

Parameters:

fieldDeclaration - of type Fields

firstN - of type int

Method Detail

getFirstN

public int getFirstN()

operate

public void operate(FlowProcess flowProcess,
           BufferCall bufferCall)

Description copied from interface: Buffer

Method operate is called once for each grouping. BufferCall passes in an Iterator that returns an argument TupleEntry for each value in the grouping defined by the argument selector on the parent Every pipe instance.

TupleEntry entry, or entry.getTuple() should not be stored directly in a collection or modified. A copy of the tuple should be made via the new Tuple( entry.getTuple() ) copy constructor.

This method is called for every unique group, whether or not there are values in the arguments Iterator.

Specified by:

operate in interface Buffer

Parameters:

flowProcess - of type FlowProcess

bufferCall - of type BufferCall