cascading.operation.aggregator
Class First

java.lang.Object
  cascading.operation.BaseOperation<Tuple[]>
      cascading.operation.aggregator.ExtentBase
          cascading.operation.aggregator.First

All Implemented Interfaces:

cascading.flow.planner.DeclaresResults, Aggregator<Tuple[]>, Operation<Tuple[]>, cascading.util.Traceable, Serializable

public class First
extends ExtentBase

Class First is an Aggregator that returns the first Tuple encountered in a grouping.

By default, it returns the first Tuple of Fields.ARGS found.

If firstN is given, Tuples with each of the first N number of Tuples encountered are returned. That is, this Aggregator will return at maximum N tuples per grouping.

Be sure to set the GroupBy sortFields to control which Tuples are seen first.

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

First()
Selects and returns the first argument Tuple encountered.

First(Fields fieldDeclaration)
Selects and returns the first argument Tuple encountered.

First(Fields fieldDeclaration, int firstN)
Selects and returns the first N argument Tuples encountered.

First(Fields fieldDeclaration, Tuple... ignoreTuples)
Selects and returns the first argument Tuple encountered, unless the Tuple is a member of the set ignoreTuples.

First(int firstN)
Selects and returns the first N argument Tuples encountered.

Method Summary

void	complete(FlowProcess flowProcess, AggregatorCall<Tuple[]> aggregatorCall) Method complete will be issued last after every TupleEntry has been passed to the Aggregator.aggregate(cascading.flow.FlowProcess, AggregatorCall) method.
int	getFirstN()
protected void	performOperation(Tuple[] context, TupleEntry entry)

Methods inherited from class cascading.operation.aggregator.ExtentBase

aggregate, equals, getIgnoreTuples, getResult, hashCode, prepare, start

Methods inherited from class cascading.operation.BaseOperation

cleanup, flush, getFieldDeclaration, getNumArgs, getTrace, isSafe, 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

Constructor Detail

First

public First()

Selects and returns the first argument Tuple encountered.

First

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

Selects and returns the first N argument Tuples encountered.

Parameters:

firstN - of type int

First

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

Selects and returns the first argument Tuple encountered.

Parameters:

fieldDeclaration - of type Fields

First

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

Selects and returns the first N argument Tuples encountered.

Parameters:

fieldDeclaration - of type Fields

firstN - of type int

First

@ConstructorProperties(value={"fieldDeclaration","ignoreTuples"})
public First(Fields fieldDeclaration,
                                        Tuple... ignoreTuples)

Selects and returns the first argument Tuple encountered, unless the Tuple is a member of the set ignoreTuples.

Parameters:

fieldDeclaration - of type Fields

ignoreTuples - of type Tuple...

Method Detail

getFirstN

public int getFirstN()

performOperation

protected void performOperation(Tuple[] context,
                                TupleEntry entry)

Specified by:

performOperation in class ExtentBase

complete

public void complete(FlowProcess flowProcess,
                     AggregatorCall<Tuple[]> aggregatorCall)

Description copied from interface: Aggregator

Method complete will be issued last after every TupleEntry has been passed to the Aggregator.aggregate(cascading.flow.FlowProcess, AggregatorCall) method. Any final calculation should be completed here and passed to the outputCollector.

Specified by:

complete in interface Aggregator<Tuple[]>

Overrides:

complete in class ExtentBase

Parameters:

flowProcess - of type FlowProcess

aggregatorCall - of type AggregatorCall