cascading.operation.aggregator
Class ExtremaBase

java.lang.Object
  cascading.operation.BaseOperation
      cascading.operation.aggregator.ExtremaBase

All Implemented Interfaces:

Aggregator, Operation, Serializable

Direct Known Subclasses:

Max, Min

public abstract class ExtremaBase
extends BaseOperation
implements Aggregator

Class ExtremaBase is the base class for Max and Min. The unique thing about Max and Min are that they return the original, un-coerced, argument value, though a coerced version of the argument is used for the comparison.

See Also:

Serialized Form

Field Summary

protected Collection

ignoreValues Field ignoreValues

Fields inherited from class cascading.operation.BaseOperation

fieldDeclaration, numArgs

Fields inherited from interface cascading.operation.Operation

ANY

Constructor Summary

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

Method Summary

void	aggregate(Map context, TupleEntry entry) Method aggregate is called for each TupleEntry value in the current grouping.
protected abstract boolean	compare(Number lhs, Number rhs)
void	complete(Map context, TupleCollector outputCollector) Method complete will be issued last after every TupleEntry has been passed to the Aggregator.aggregate(Map, TupleEntry) method.
protected abstract double	getInitialValue()
void	start(Map context, TupleEntry groupEntry) Method start initializes the aggregation procedure.

Methods inherited from class cascading.operation.BaseOperation

getFieldDeclaration, getNumArgs, printOperationInternal, toString, toStringInternal

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface cascading.operation.Operation

getFieldDeclaration, getNumArgs

Field Detail

ignoreValues

protected final Collection ignoreValues

Field ignoreValues

Constructor Detail

ExtremaBase

public ExtremaBase(Fields fieldDeclaration)

ExtremaBase

public ExtremaBase(int numArgs,
                   Fields fieldDeclaration)

ExtremaBase

protected ExtremaBase(Fields fieldDeclaration,
                      Object... ignoreValues)

Method Detail

start

public void start(Map context,
                  TupleEntry groupEntry)

Description copied from interface: Aggregator

Method start initializes the aggregation procedure. The Map context is used to hold intermediate values. The context should be initialized here if necessary. This method will be called before Aggregator.aggregate(Map, TupleEntry) and Aggregator.complete(java.util.Map,cascading.tuple.TupleCollector).

TupleEntry groupEntry, or groupEntry.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:

start in interface Aggregator

Parameters:

context - the map to be initialized (if necessary)

groupEntry - is the current grouping tuple

See Also:

Aggregator.start(java.util.Map , cascading.tuple.TupleEntry)

getInitialValue

protected abstract double getInitialValue()

aggregate

public void aggregate(Map context,
                      TupleEntry entry)

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

Parameters:

context - the map with aggregate values so far

entry - the tuple entry to add to the operation

See Also:

Aggregator.aggregate(java.util.Map, cascading.tuple.TupleEntry)

compare

protected abstract boolean compare(Number lhs,
                                   Number rhs)

complete

public void complete(Map context,
                     TupleCollector outputCollector)

Description copied from interface: Aggregator

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

Specified by:

complete in interface Aggregator

Parameters:

context - the aggregate map @return the final aggregate value

See Also:

Aggregator.complete(java.util.Map, cascading.tuple.TupleCollector)