Class GroupAggregator

The GroupAggregator provides an ability to split a subset of entries in an IInvocableCache into a collection of non-intersecting subsets and then aggregate them separately and independently.

Inheritance

object

GroupAggregator

GroupAggregator.Parallel

Implements

IEntryAggregator

IPortableObject

Inherited Members

object.Equals(object, object)

object.GetType()

object.MemberwiseClone()

object.ReferenceEquals(object, object)

Namespace: Tangosol.Util.Aggregator

Assembly: Coherence.dll

Syntax

public class GroupAggregator : IEntryAggregator, IPortableObject

Remarks

The splitting (grouping) is performed using the results of the underlying IValueExtractor in such a way that two entries will belong to the same group if and only if the result of the corresponding Extract(object) 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 dictionary 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 IFilter object.

Informally speaking, this aggregator is analogous to the SQL "group by" and "having" clauses. Note that the "having" IFilter 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 IEntryAggregator implementations that are constructed directly, instances of GroupAggregator should only be created using one of the factory methods:

CreateInstance(IValueExtractor, IEntryAggregator) CreateInstance(IValueExtractor, IEntryAggregator, IFilter) CreateInstance(string, IEntryAggregator) CreateInstance(string, IEntryAggregator, IFilter)

Constructors

GroupAggregator()

Default constructor.

Declaration

public GroupAggregator()

GroupAggregator(IValueExtractor, IEntryAggregator, IFilter)

Construct a GroupAggregator based on a specified IValueExtractor and underlying IEntryAggregator.

Declaration

protected GroupAggregator(IValueExtractor extractor, IEntryAggregator aggregator, IFilter filter)

Parameters

Type	Name	Description
IValueExtractor	extractor	An IValueExtractor object that is used to split IInvocableCache entries into non-intersecting subsets; may not be null.
IEntryAggregator	aggregator	An IEntryAggregator object; may not be null.
IFilter	filter	An optional IFilter object used to filter out results of individual group aggregation results.

Fields

m_aggregator

The underlying IEntryAggregator.

Declaration

protected IEntryAggregator m_aggregator

Field Value

Type	Description
IEntryAggregator

m_extractor

The underlying IValueExtractor.

Declaration

protected IValueExtractor m_extractor

Field Value

Type	Description
IValueExtractor

m_filter

The IFilter object representing the "having" clause of this "group by" aggregator.

Declaration

protected IFilter m_filter

Field Value

Type	Description
IFilter

Properties

Aggregator

Obtain the underlying IEntryAggregator.

Declaration

public virtual IEntryAggregator Aggregator { get; }

Property Value

Type	Description
IEntryAggregator	The underlying IEntryAggregator.

Extractor

Obtain the underlying IValueExtractor.

Declaration

public virtual IValueExtractor Extractor { get; }

Property Value

Type	Description
IValueExtractor	The underlying IValueExtractor.

Methods

Aggregate(ICollection)

Process a collection of IInvocableCacheEntry objects using the underlying extractor to split the entries into non-intersecting (distinct) groups and then apply the underlying aggregator separately to each group.

Declaration

public virtual object Aggregate(ICollection entries)

Parameters

Type	Name	Description
ICollection	entries	A collection of read-only IInvocableCacheEntry objects to aggregate.

Returns

Type	Description
object	A dictionary that has the unique tuples as keys and results of the corresponding subset aggregation as values.

CreateInstance(string, IEntryAggregator)

Create an instance of GroupAggregator based on a specified member name(s) and an IEntryAggregator.

Declaration

public static GroupAggregator CreateInstance(string member, IEntryAggregator aggregator)

Parameters

Type	Name	Description
string	member	A member name or a comma-delimited sequence of names that results in a ReflectionExtractor or a MultiExtractor that will be used to split IInvocableCache entries into distinct groups.
IEntryAggregator	aggregator	An underlying IEntryAggregator.

Returns

Type	Description
GroupAggregator	An instance of GroupAggregator based on a specified member name(s) and an IEntryAggregator.

Remarks

If the specified underlying aggregator is an instance of IParallelAwareAggregator, 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.

CreateInstance(string, IEntryAggregator, IFilter)

Create an instance of GroupAggregator based on a specified member name(s), an IEntryAggregator and a result evaluation filter.

Declaration

public static GroupAggregator CreateInstance(string member, IEntryAggregator aggregator, IFilter filter)

Parameters

Type	Name	Description
string	member	A member name or a comma-delimited sequence of names that results in a ReflectionExtractor or a MultiExtractor that will be used to split IInvocableCache entries into distinct groups.
IEntryAggregator	aggregator	An underlying IEntryAggregator.
IFilter	filter	An optional IFilter object that will be used to evaluate results of each individual group aggregation.

Returns

Type	Description
GroupAggregator	An instance of GroupAggregator based on a specified member name(s), an IEntryAggregator and a result evaluation filter.

Remarks

If the specified underlying aggregator is an instance of IParallelAwareAggregator, 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.

CreateInstance(IValueExtractor, IEntryAggregator)

Create an instance of GroupAggregator based on a specified extractor and an IEntryAggregator.

Declaration

public static GroupAggregator CreateInstance(IValueExtractor extractor, IEntryAggregator aggregator)

Parameters

Type	Name	Description
IValueExtractor	extractor	An IValueExtractor that will be used to split a set of IInvocableDictionary entries into distinct groups.
IEntryAggregator	aggregator	An underlying IEntryAggregator.

Returns

Type	Description
GroupAggregator	An instance of GroupAggregator based on a specified extractor and an IEntryAggregator.

Remarks

If the specified aggregator is an instance of IParallelAwareAggregator, 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.

CreateInstance(IValueExtractor, IEntryAggregator, IFilter)

Create an instance of GroupAggregator based on a specified extractor and an IEntryAggregator and a result evaluation filter.

Declaration

public static GroupAggregator CreateInstance(IValueExtractor extractor, IEntryAggregator aggregator, IFilter filter)

Parameters

Type	Name	Description
IValueExtractor	extractor	An IValueExtractor that will be used to split a set of IInvocableDictionary entries into distinct groups.
IEntryAggregator	aggregator	An underlying IEntryAggregator.
IFilter	filter	An optional IFilter object used to filter out results of individual group aggregation results.

Returns

Type	Description
GroupAggregator	An instance of GroupAggregator based on a specified extractor and an IEntryAggregator and a result evaluation filter.

Remarks

If the specified aggregator is an instance of IParallelAwareAggregator, 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.

Equals(object)

Compare the GroupAggregator with another object to determine equality.

Declaration

public override bool Equals(object o)

Parameters

Type	Name	Description
object	o	The GroupAggregator to compare to.

Returns

Type	Description
bool	true if this GroupAggregator and the passed object are equivalent.

Overrides

object.Equals(object)

GetHashCode()

Determine a hash value for the GroupAggregator object according to the general object.GetHashCode() contract.

Declaration

public override int GetHashCode()

Returns

Type	Description
int	An integer hash value for this GroupAggregator object.

Overrides

object.GetHashCode()

ReadExternal(IPofReader)

Restore the contents of a user type instance by reading its state using the specified IPofReader object.

Declaration

public virtual void ReadExternal(IPofReader reader)

Parameters

Type	Name	Description
IPofReader	reader	The IPofReader from which to read the object's state.

Exceptions

Type	Condition
IOException	If an I/O error occurs.

ToString()

Return a human-readable description for this GroupAggregator.

Declaration

public override string ToString()

Returns

Type	Description
string	A string description of the GroupAggregator.

Overrides

object.ToString()

WriteExternal(IPofWriter)

Save the contents of a POF user type instance by writing its state using the specified IPofWriter object.

Declaration

public virtual void WriteExternal(IPofWriter writer)

Parameters

Type	Name	Description
IPofWriter	writer	The IPofWriter to which to write the object's state.

Exceptions

Type	Condition
IOException	If an I/O error occurs.

Implements

IEntryAggregator

IPortableObject