com.bigdata.bop.rdf.aggregate
Class COUNT

java.lang.Object
  com.bigdata.bop.CoreBaseBOp
      com.bigdata.bop.BOpBase
          com.bigdata.bop.ImmutableBOp
              com.bigdata.bop.aggregate.AggregateBase<IV>
                  com.bigdata.bop.rdf.aggregate.COUNT

All Implemented Interfaces:

IAggregate<IV>, BOp, IValueExpression<IV>, IPropertySet, Serializable, Cloneable

public class COUNT
extends AggregateBase<IV>

Operator computes the number of non-null values over the presented binding sets for the given variable.

Note: COUNT(*) is the cardinality of the solution multiset. COUNT(DISTINCT *) is the cardinality of the distinct solutions in the solution multiset. These semantics are not directly handled by this class. It relies on the aggregation operator to compute those values.

Author:

thompsonbry

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from class com.bigdata.bop.aggregate.AggregateBase

AggregateBase.Annotations

Field Summary

Fields inherited from class com.bigdata.bop.aggregate.AggregateBase

EMPTY_LITERAL, ZERO

Fields inherited from class com.bigdata.bop.CoreBaseBOp

DEFAULT_INITIAL_CAPACITY

Fields inherited from interface com.bigdata.bop.BOp

NOANNS, NOARGS

Constructor Summary

COUNT(boolean distinct, IValueExpression<IV> expr)

COUNT(BOp[] args, Map<String,Object> annotations)

COUNT(COUNT op)

Method Summary

IV	done() Return the final value.
IV	get(IBindingSet bindingSet) Return the current value of the aggregate (this has a side-effect on the internal state of the IAggregate operator).
INeedsMaterialization.Requirement	getRequirement() COUNT does not need to actually see the materialized values, or even the IVs.
void	reset() Reset the aggregate's internal state.

Methods inherited from class com.bigdata.bop.aggregate.AggregateBase

isDistinct, isWildcard

Methods inherited from class com.bigdata.bop.ImmutableBOp

_clearProperty, _setProperty

Methods inherited from class com.bigdata.bop.BOpBase

_set, annotations, annotationsCopy, annotationsEqual, annotationsRef, argIterator, args, argsCopy, arity, clearAnnotations, clearProperty, deepCopy, deepCopy, get, getProperty, setArg, setProperty, setUnboundProperty, toArray, toArray

Methods inherited from class com.bigdata.bop.CoreBaseBOp

annotationsEqual, annotationsToString, checkArgs, clone, equals, getEvaluationContext, getId, getProperty, getRequiredProperty, hashCode, indent, isController, toShortString, toString

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface com.bigdata.bop.BOp

annotations, argIterator, args, arity, clone, get, getEvaluationContext, getId, getProperty, getRequiredProperty, isController, setProperty, toArray, toArray, toShortString, toString

Methods inherited from interface cutthecrap.utils.striterators.IPropertySet

getProperty

Constructor Detail

COUNT

public COUNT(COUNT op)

COUNT

public COUNT(BOp[] args,
             Map<String,Object> annotations)

COUNT

public COUNT(boolean distinct,
             IValueExpression<IV> expr)

Method Detail

get

public IV get(IBindingSet bindingSet)

Return the current value of the aggregate (this has a side-effect on the internal state of the IAggregate operator). Functions which can not produce an intermediate result, such as AVERAGE, MAY return null.

Note: If evaluation of the IAggregate throws an error, then that error must be "sticky" and reported out by IAggregate.done() as well. This contract is relied on to correctly propagate errors within a group when using incremental (pipelined) evaluation of IAggregates. The error state is cleared by IAggregate.reset().

Operation is not implemented by this class and must be overridden if the AggregateBase is to be directly evaluated. However, note that the computation of aggregate functions is often based on hard coded recognition of the appropriate function code.

Note: DISTINCT is merely carried as a marker on COUNT (and the other aggregate functions). The application of DISTINCT to the inner expression to form a column projection is handled by the driving evaluation logic rather than by AggregateBase.get(IBindingSet).

Note: COUNT() returns ZERO if there are no non-error solutions presented. This assumes that the ZERO will be an xsd:long.

Specified by:

get in interface IAggregate<IV>

Specified by:

get in interface IValueExpression<IV>

Overrides:

get in class AggregateBase<IV>

Parameters:

bindingSet - The binding set.

Returns:

The as bound value of the constant, variable, or expression.

reset

public void reset()

Description copied from interface: IAggregate

Reset the aggregate's internal state.

done

public IV done()

Description copied from interface: IAggregate

Return the final value.

getRequirement

public INeedsMaterialization.Requirement getRequirement()

COUNT does not need to actually see the materialized values, or even the IVs. COUNT(DISTINCT) does need to see the IVs, but they still do not need to be materialized.