com.tangosol.util.aggregator
Class DistinctValues

java.lang.Object
  com.tangosol.util.Base
      com.tangosol.util.BitHelper
          com.tangosol.util.ExternalizableHelper
              com.tangosol.util.aggregator.AbstractAggregator
                  com.tangosol.util.aggregator.DistinctValues

All Implemented Interfaces:

ExternalizableLite, PortableObject, InvocableMap.EntryAggregator, InvocableMap.ParallelAwareAggregator, Serializable

public class DistinctValues
extends AbstractAggregator

Return the set of unique values extracted from a set of entries in a Map. If the set of entries is empty, an empty set is returned.

This aggregator could be used in combination with MultiExtractor allowing to collect all unique combinations (tuples) of a given set of attributes.

The DistinctValues aggregator covers a simple case of a more generic aggregation pattern implemented by the GroupAggregator, which in addition to collecting all distinct values or tuples, runs an aggregation against each distinct entry set (group).

Author:

jh 2005.12.20

Field Summary

protected Set

m_set The resulting set of distinct values.

Fields inherited from class com.tangosol.util.aggregator.AbstractAggregator

m_fParallel

Constructor Summary

DistinctValues()
Default constructor (necessary for the ExternalizableLite interface).

DistinctValues(String sMethod)
Construct an DistinctValues aggregator.

DistinctValues(ValueExtractor extractor)
Construct a DistinctValues aggregator.

Method Summary

protected Set	ensureSet() Return a set that can be used to store distinct values, creating it if one has not already been created.
protected Object	finalizeResult(boolean fFinal) Obtain the result of the aggregation.
protected void	init(boolean fFinal) Initialize the aggregation result.
protected void	process(Object o, boolean fFinal) Incorporate one aggregatable value into the result.

Methods inherited from class com.tangosol.util.aggregator.AbstractAggregator

aggregate, aggregateResults, equals, getParallelAggregator, getValueExtractor, hashCode, readExternal, readExternal, toString, writeExternal, writeExternal

Methods inherited from class com.tangosol.util.BitHelper

countBits, countBits, countBits, indexOfLSB, indexOfLSB, indexOfLSB, indexOfMSB, indexOfMSB, indexOfMSB, toBitString, toBitString, toBitString

Field Detail

m_set

protected transient Set m_set

The resulting set of distinct values.

Constructor Detail

DistinctValues

public DistinctValues()

Default constructor (necessary for the ExternalizableLite interface).

DistinctValues

public DistinctValues(ValueExtractor extractor)

Construct a DistinctValues aggregator.

Parameters:

extractor - the extractor that provides a value in the form of any Java object

DistinctValues

public DistinctValues(String sMethod)

Construct an DistinctValues aggregator.

Parameters:

sMethod - the name of the method that returns a value in the form of any Java object

Method Detail

init

protected void init(boolean fFinal)

Initialize the aggregation result.

Specified by:

init in class AbstractAggregator

Parameters:

fFinal - true is passed if the aggregation process that is being initialized must produce a final aggregation result; this will only be false if a parallel approach is being used and the initial (partial) aggregation process is being initialized

process

protected void process(Object o,
                       boolean fFinal)

Incorporate one aggregatable value into the result.

If the fFinal parameter is true, the given object is a partial result (returned by an individual parallel aggregator) that should be incorporated into the final result; otherwise, the object is a value extracted from an InvocableMap.Entry.

Specified by:

process in class AbstractAggregator

Parameters:

o - the value to incorporate into the aggregated result

fFinal - true to indicate that the given object is a partial result returned by a parallel aggregator

finalizeResult

protected Object finalizeResult(boolean fFinal)

Obtain the result of the aggregation.

If the fFinal parameter is true, the returned object must be the final result of the aggregation; otherwise, the returned object will be treated as a partial result that should be incorporated into the final result.

Specified by:

finalizeResult in class AbstractAggregator

Parameters:

fFinal - true to indicate that the final result of the aggregation process should be returned; this will only be false if a parallel approach is being used

Returns:

the result of the aggregation process

ensureSet

protected Set ensureSet()

Return a set that can be used to store distinct values, creating it if one has not already been created.

Returns:

a set that can be used to store distinct values