Oracle® Coherence Java API Reference
v3.5.3

E15583-01

com.tangosol.util.aggregator
Class GroupAggregator

java.lang.Object
  extended by com.tangosol.util.Base
      extended by com.tangosol.util.BitHelper
          extended by com.tangosol.util.ExternalizableHelper
              extended by com.tangosol.util.aggregator.GroupAggregator
All Implemented Interfaces:
ExternalizableLite, PortableObject, InvocableMap.EntryAggregator, java.io.Serializable
Direct Known Subclasses:
GroupAggregator.Parallel

public class GroupAggregator
extends ExternalizableHelper
implements InvocableMap.EntryAggregator, ExternalizableLite, PortableObject

The GroupAggregator provides an ability to split a subset of entries in an InvocableMap into a collection of non-intersecting subsets and then aggregate them separately and independently. The splitting (grouping) is performed using the results of the underlying ValueExtractor in such a way that two entries will belong to the same group if and only if the result of the corresponding extract call produces the same value or tuple (list of values). After the entries are split into the groups, the underlying aggregator is applied separately to each group. The result of the aggregation by the GroupAggregator is a Map that has distinct values (or tuples) as keys and results of the individual aggregation as values. Additionally, those results could be further reduced using an optional Filter object.

Informally speaking, this aggregator is analogous to the SQL "group by" and "having" clauses. Note that the "having" Filter is applied independently on each server against the partial aggregation results; this generally implies that data affinity is required to ensure that all required data used to generate a given result exists within a single cache partition. In other words, the "group by" predicate should not span multiple partitions if the "having" clause is used.

The GroupAggregator is somewhat similar to the DistinctValues aggregator, which returns back a list of distinct values (tuples) without performing any additional aggregation work.

Unlike many other concrete EntryAggregator implementations that are constructed directly, instances of GroupAggregator should only be created using one of the factory methods: createInstance(extractor, aggregator), createInstance(extractor, aggregator, filter), createInstance(sMethod, aggregator) createInstance(sMethod, aggregator, filter)

Since:
Coherence 3.2
Author:
gg 2006.02.15

Nested Class Summary
static class GroupAggregator.Parallel
          Parallel implementation of the GroupAggregator.
 
Field Summary
protected  InvocableMap.EntryAggregator m_aggregator
          The underlying EntryAggregator.
protected  ValueExtractor m_extractor
          The underlying ValueExtractor.
protected  Filter m_filter
          The Filter object representing the "having" clause of this "group by" aggregator.
 
Constructor Summary
  GroupAggregator()
          Default constructor (necessary for the ExternalizableLite interface).
protected GroupAggregator(ValueExtractor extractor, InvocableMap.EntryAggregator aggregator, Filter filter)
          Construct a GroupAggregator based on a specified ValueExtractor and underlying EntryAggregator.
 
Method Summary
 java.lang.Object aggregate(java.util.Set setEntries)
          Process a set of InvocableMap Entry objects using the underlying extractor to split the entries into non-intersecting (distinct) groups and then apply the underlying aggregator separately to each group.
static GroupAggregator createInstance(java.lang.String sMethod, InvocableMap.EntryAggregator aggregator)
          Create an instance of GroupAggregator based on a specified method name(s) and an EntryAggregator.
static GroupAggregator createInstance(java.lang.String sMethod, InvocableMap.EntryAggregator aggregator, Filter filter)
          Create an instance of GroupAggregator based on a specified method name(s), an EntryAggregator and a result evaluation filter.
static GroupAggregator createInstance(ValueExtractor extractor, InvocableMap.EntryAggregator aggregator)
          Create an instance of GroupAggregator based on a specified extractor and an EntryAggregator.
static GroupAggregator createInstance(ValueExtractor extractor, InvocableMap.EntryAggregator aggregator, Filter filter)
          Create an instance of GroupAggregator based on a specified extractor and an EntryAggregator and a result evaluation filter.
 boolean equals(java.lang.Object o)
          Compare the GroupAggregator with another object to determine equality.
 InvocableMap.EntryAggregator getAggregator()
          Obtain the underlying EntryAggregator.
 ValueExtractor getExtractor()
          Obtain the underlying ValueExtractor.
 int hashCode()
          Determine a hash value for the GroupAggregator object according to the general Object.hashCode() contract.
 void readExternal(java.io.DataInput in)
          Restore the contents of this object by loading the object's state from the passed DataInput object.
 void readExternal(PofReader in)
          Restore the contents of a user type instance by reading its state using the specified PofReader object.
 java.lang.String toString()
          Return a human-readable description for this GroupAggregator.
 void writeExternal(java.io.DataOutput out)
          Save the contents of this object by storing the object's state into the passed DataOutput object.
 void writeExternal(PofWriter out)
          Save the contents of a POF user type instance by writing its state using the specified PofWriter object.
 
Methods inherited from class com.tangosol.util.BitHelper
countBits, countBits, countBits, indexOfLSB, indexOfLSB, indexOfLSB, indexOfMSB, indexOfMSB, indexOfMSB, rotateLeft, rotateLeft, rotateLeft, rotateRight, rotateRight, rotateRight, toBitString, toBitString, toBitString
 

Field Detail

m_extractor

protected ValueExtractor m_extractor
The underlying ValueExtractor.


m_aggregator

protected InvocableMap.EntryAggregator m_aggregator
The underlying EntryAggregator.


m_filter

protected Filter m_filter
The Filter object representing the "having" clause of this "group by" aggregator.

Constructor Detail

GroupAggregator

public GroupAggregator()
Default constructor (necessary for the ExternalizableLite interface).


GroupAggregator

protected GroupAggregator(ValueExtractor extractor,
                          InvocableMap.EntryAggregator aggregator,
                          Filter filter)
Construct a GroupAggregator based on a specified ValueExtractor and underlying EntryAggregator.

Parameters:
extractor - a ValueExtractor object that is used to split InvocableMap entries into non-itersecting subsets; may not be null
aggregator - an EntryAggregator object; may not be null
filter - an optional Filter object used to filter out results of individual group aggregation results
Method Detail

aggregate

public java.lang.Object aggregate(java.util.Set setEntries)
Process a set of InvocableMap Entry objects using the underlying extractor to split the entries into non-intersecting (distinct) groups and then apply the underlying aggregator separately to each group.

Specified by:
aggregate in interface InvocableMap.EntryAggregator
Parameters:
setEntries - a Set of read-only InvocableMap Entry objects to aggregate
Returns:
a Map that has the unique tuples as keys and results of the corresponding subset aggregation as values

readExternal

public void readExternal(java.io.DataInput in)
                  throws java.io.IOException
Restore the contents of this object by loading the object's state from the passed DataInput object.

Specified by:
readExternal in interface ExternalizableLite
Parameters:
in - the DataInput stream to read data from in order to restore the state of this object
Throws:
java.io.IOException - if an I/O exception occurs
java.io.NotActiveException - if the object is not in its initial state, and therefore cannot be deserialized into

writeExternal

public void writeExternal(java.io.DataOutput out)
                   throws java.io.IOException
Save the contents of this object by storing the object's state into the passed DataOutput object.

Specified by:
writeExternal in interface ExternalizableLite
Parameters:
out - the DataOutput stream to write the state of this object to
Throws:
java.io.IOException - if an I/O exception occurs

readExternal

public void readExternal(PofReader in)
                  throws java.io.IOException
Restore the contents of a user type instance by reading its state using the specified PofReader object.

Specified by:
readExternal in interface PortableObject
Parameters:
in - the PofReader from which to read the object's state
Throws:
java.io.IOException - if an I/O error occurs

writeExternal

public void writeExternal(PofWriter out)
                   throws java.io.IOException
Save the contents of a POF user type instance by writing its state using the specified PofWriter object.

Specified by:
writeExternal in interface PortableObject
Parameters:
out - the PofWriter to which to write the object's state
Throws:
java.io.IOException - if an I/O error occurs

getExtractor

public ValueExtractor getExtractor()
Obtain the underlying ValueExtractor.

Returns:
the underlying ValueExtractor

getAggregator

public InvocableMap.EntryAggregator getAggregator()
Obtain the underlying EntryAggregator.

Returns:
the underlying EntryAggregator

equals

public boolean equals(java.lang.Object o)
Compare the GroupAggregator with another object to determine equality.

Returns:
true iff this GroupAggregator and the passed object are equivalent

hashCode

public int hashCode()
Determine a hash value for the GroupAggregator object according to the general Object.hashCode() contract.

Returns:
an integer hash value for this GroupAggregator object

toString

public java.lang.String toString()
Return a human-readable description for this GroupAggregator.

Returns:
a String description of the GroupAggregator

createInstance

public static GroupAggregator createInstance(java.lang.String sMethod,
                                             InvocableMap.EntryAggregator aggregator)
Create an instance of GroupAggregator based on a specified method name(s) and an EntryAggregator.
If the specified underlying aggregator is an instance of ParallelAwareAggregator, then a parallel-aware instance of the GroupAggregator will be created. Otherwise, the resulting GroupAggregator will not be parallel-aware and could be ill-suited for aggregations run against large partitioned caches.

Parameters:
sMethod - a method name or a comma-delimited sequence of names that results in a ReflectionExtractor or a MultiExtractor that will be used to split InvocableMap entries into distinct groups
aggregator - an underlying EntryAggregator

createInstance

public static GroupAggregator createInstance(java.lang.String sMethod,
                                             InvocableMap.EntryAggregator aggregator,
                                             Filter filter)
Create an instance of GroupAggregator based on a specified method name(s), an EntryAggregator and a result evaluation filter.
If the specified underlying aggregator is an instance of ParallelAwareAggregator, then a parallel-aware instance of the GroupAggregator will be created. Otherwise, the resulting GroupAggregator will not be parallel-aware and could be ill-suited for aggregations run against large partitioned caches.

Parameters:
sMethod - a method name or a comma-delimited sequence of names that results in a ReflectionExtractor or a MultiExtractor that will be used to split InvocableMap entries into distinct groups
aggregator - an underlying EntryAggregator
filter - an optional Filter object that will be used to evaluate results of each individual group aggregation

createInstance

public static GroupAggregator createInstance(ValueExtractor extractor,
                                             InvocableMap.EntryAggregator aggregator)
Create an instance of GroupAggregator based on a specified extractor and an EntryAggregator.
If the specified aggregator is an instance of ParallelAwareAggregator, then a parallel-aware instance of the GroupAggregator will be created. Otherwise, the resulting GroupAggregator will not be parallel-aware and could be ill-suited for aggregations run against large partitioned caches.

Parameters:
extractor - a ValueExtractor that will be used to split a set of InvocableMap entries into distinct groups
aggregator - an underlying EntryAggregator

createInstance

public static GroupAggregator createInstance(ValueExtractor extractor,
                                             InvocableMap.EntryAggregator aggregator,
                                             Filter filter)
Create an instance of GroupAggregator based on a specified extractor and an EntryAggregator and a result evaluation filter.
If the specified aggregator is an instance of ParallelAwareAggregator, then a parallel-aware instance of the GroupAggregator will be created. Otherwise, the resulting GroupAggregator will not be parallel-aware and could be ill-suited for aggregations run against large partitioned caches.

Parameters:
extractor - a ValueExtractor that will be used to split a set of InvocableMap entries into distinct groups
aggregator - an underlying EntryAggregator
filter - an optional Filter object used to filter out results of individual group aggregation results

Oracle® Coherence Java API Reference
v3.5.3

E15583-01

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