cascading.operation.aggregator
Class ExtremaValueBase

java.lang.Object
  cascading.operation.BaseOperation<ExtremaValueBase.Context>
      cascading.operation.aggregator.ExtremaValueBase

All Implemented Interfaces:

DeclaresResults, Aggregator<ExtremaValueBase.Context>, Operation<ExtremaValueBase.Context>, Serializable

Direct Known Subclasses:

MaxValue, MinValue

public abstract class ExtremaValueBase
extends BaseOperation<ExtremaValueBase.Context>
implements Aggregator<ExtremaValueBase.Context>

Class ExtremaValueBase is the base class for MaxValue and MinValue where the values are expected to by Comparable types and the Comparable.compareTo(Object) result is use for max/min comparison.

See Also:

Serialized Form

Nested Class Summary

protected static class

ExtremaValueBase.Context

Field Summary

protected Collection

ignoreValues Field ignoreValues

Fields inherited from class cascading.operation.BaseOperation

fieldDeclaration, numArgs, trace

Fields inherited from interface cascading.operation.Operation

ANY

Constructor Summary

	ExtremaValueBase(Fields fieldDeclaration)
protected	ExtremaValueBase(Fields fieldDeclaration, Object... ignoreValues)
	ExtremaValueBase(int numArgs, Fields fieldDeclaration)

Method Summary

void	aggregate(FlowProcess flowProcess, AggregatorCall<ExtremaValueBase.Context> aggregatorCall) Method aggregate is called for each TupleEntry value in the current grouping.
protected abstract boolean	compare(Comparable lhs, Comparable rhs) Allows subclasses to provide own comparison method.
void	complete(FlowProcess flowProcess, AggregatorCall<ExtremaValueBase.Context> aggregatorCall) Method complete will be issued last after every TupleEntry has been passed to the Aggregator.aggregate(cascading.flow.FlowProcess, AggregatorCall) method.
boolean	equals(Object object)
Collection	getIgnoreValues()
protected Tuple	getResult(AggregatorCall<ExtremaValueBase.Context> aggregatorCall)
int	hashCode()
void	prepare(FlowProcess flowProcess, OperationCall<ExtremaValueBase.Context> operationCall) Method prepare does nothing, and may safely be overridden.
void	start(FlowProcess flowProcess, AggregatorCall<ExtremaValueBase.Context> aggregatorCall) Method start initializes the aggregation procedure and is called for every unique grouping.

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

Field Detail

ignoreValues

protected final Collection ignoreValues

Field ignoreValues

Constructor Detail

ExtremaValueBase

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

ExtremaValueBase

@ConstructorProperties(value={"numArgs","fieldDeclaration"})
public ExtremaValueBase(int numArgs,
                                                   Fields fieldDeclaration)

ExtremaValueBase

@ConstructorProperties(value={"fieldDeclaration","ignoreValues"})
protected ExtremaValueBase(Fields fieldDeclaration,
                                                      Object... ignoreValues)

Method Detail

getIgnoreValues

public Collection getIgnoreValues()

prepare

public void prepare(FlowProcess flowProcess,
                    OperationCall<ExtremaValueBase.Context> operationCall)

Description copied from class: BaseOperation

Method prepare does nothing, and may safely be overridden.

Specified by:

prepare in interface Operation<ExtremaValueBase.Context>

Overrides:

prepare in class BaseOperation<ExtremaValueBase.Context>

start

public void start(FlowProcess flowProcess,
                  AggregatorCall<ExtremaValueBase.Context> aggregatorCall)

Description copied from interface: Aggregator

Method start initializes the aggregation procedure and is called for every unique grouping.

The AggregatorCall context should be initialized here if necessary.

The first time this method is called for a given 'process', the AggregatorCall context will be null. This method should set a new instance of the user defined context object. When the AggregatorCall context is not null, it is up to the developer to create a new instance, or 'recycle' the given instance. If recycled, it must be re-initialized to remove any previous state/values.

For example, if a Map is used to hold the intermediate data for each subsequent Aggregator.aggregate(cascading.flow.FlowProcess, AggregatorCall) call, new HashMap() should be set on the AggregatorCall instance when OperationCall.getContext() is null. On the next grouping, start() will be called again, but this time with the old Map instance. In this case, map.clear() should be invoked before returning.

Specified by:

start in interface Aggregator<ExtremaValueBase.Context>

Parameters:

flowProcess - of type FlowProcess

aggregatorCall - of type AggregatorCall

aggregate

public void aggregate(FlowProcess flowProcess,
                      AggregatorCall<ExtremaValueBase.Context> aggregatorCall)

Description copied from interface: Aggregator

Method aggregate is called for each TupleEntry value in the current grouping.

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

Specified by:

aggregate in interface Aggregator<ExtremaValueBase.Context>

Parameters:

flowProcess - of type FlowProcess

aggregatorCall - of type AggregatorCall

compare

protected abstract boolean compare(Comparable lhs,
                                   Comparable rhs)

Allows subclasses to provide own comparison method.

Parameters:

lhs - Comparable type

rhs - Comparable type

Returns:

true if the rhs should be retained as the result value

complete

public void complete(FlowProcess flowProcess,
                     AggregatorCall<ExtremaValueBase.Context> 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<ExtremaValueBase.Context>

Parameters:

flowProcess - of type FlowProcess

aggregatorCall - of type AggregatorCall

getResult

protected Tuple getResult(AggregatorCall<ExtremaValueBase.Context> aggregatorCall)

equals

public boolean equals(Object object)

Overrides:

equals in class BaseOperation<ExtremaValueBase.Context>

hashCode

public int hashCode()

Overrides:

hashCode in class BaseOperation<ExtremaValueBase.Context>