Utility class for calculating aggregates for a field (or expression) over the features from a vector layer. More...

#include <qgsaggregatecalculator.h>

Classes
struct	AggregateInfo
	Structured information about the available aggregates. More...

struct	AggregateParameters
	A bundle of parameters controlling aggregate calculation. More...

Public Types
enum	Aggregate { Count , CountDistinct , CountMissing , Min , Max , Sum , Mean , Median , StDev , StDevSample , Range , Minority , Majority , FirstQuartile , ThirdQuartile , InterQuartileRange , StringMinimumLength , StringMaximumLength , StringConcatenate , GeometryCollect , ArrayAggregate , StringConcatenateUnique }
	Available aggregates to calculate. More...

Public Member Functions
	QgsAggregateCalculator (const QgsVectorLayer *layer)
	Constructor for QgsAggregateCalculator. More...

QVariant	calculate (Aggregate aggregate, const QString &fieldOrExpression, QgsExpressionContext context=nullptr, bool ok=nullptr, QgsFeedback *feedback=nullptr) const
	Calculates the value of an aggregate. More...

QString	delimiter () const
	Returns the delimiter used for joining values with the StringConcatenate aggregate. More...

QString	filter () const
	Returns the filter which limits the features used during the aggregate calculation. More...

QString	lastError () const
	Returns the last error encountered during the aggregate calculation. More...

const QgsVectorLayer *	layer () const
	Returns the associated vector layer. More...

void	setDelimiter (const QString &delimiter)
	Sets the delimiter to use for joining values with the StringConcatenate aggregate. More...

void	setFidsFilter (const QgsFeatureIds &fids)
	Sets a filter to limit the features used during the aggregate calculation. More...

void	setFilter (const QString &filterExpression)
	Sets a filter to limit the features used during the aggregate calculation. More...

void	setParameters (const AggregateParameters &parameters)
	Sets all aggregate parameters from a parameter bundle. More...

Static Public Member Functions
static QList< QgsAggregateCalculator::AggregateInfo >	aggregates ()
	Structured information for available aggregates. More...

static QString	displayName (Aggregate aggregate)
	Returns the friendly display name for a aggregate. More...

static Aggregate	stringToAggregate (const QString &string, bool *ok=nullptr)
	Converts a string to a aggregate type. More...

Detailed Description

Utility class for calculating aggregates for a field (or expression) over the features from a vector layer.

It is recommended that QgsVectorLayer::aggregate() is used rather then directly using this class, as the QgsVectorLayer method can handle delegating aggregate calculation to a data provider for remote calculation.

Since: QGIS 2.16

Definition at line 44 of file qgsaggregatecalculator.h.

Member Enumeration Documentation

◆ Aggregate

enum QgsAggregateCalculator::Aggregate

Available aggregates to calculate.

Not all aggregates are available for all field types.

Enumerator
Count	Count.
CountDistinct	Number of distinct values.
CountMissing	Number of missing (null) values.
Min	Min of values.
Max	Max of values.
Sum	Sum of values.
Mean	Mean of values (numeric fields only)
Median	Median of values (numeric fields only)
StDev	Standard deviation of values (numeric fields only)
StDevSample	Sample standard deviation of values (numeric fields only)
Range	Range of values (max - min) (numeric and datetime fields only)
Minority	Minority of values.
Majority	Majority of values.
FirstQuartile	First quartile (numeric fields only)
ThirdQuartile	Third quartile (numeric fields only)
InterQuartileRange	Inter quartile range (IQR) (numeric fields only)
StringMinimumLength	Minimum length of string (string fields only)
StringMaximumLength	Maximum length of string (string fields only)
StringConcatenate	Concatenate values with a joining string (string fields only). Specify the delimiter using setDelimiter().
GeometryCollect	Create a multipart geometry from aggregated geometries.
ArrayAggregate	Create an array of values.
StringConcatenateUnique	Concatenate unique values with a joining string (string fields only). Specify the delimiter using setDelimiter().

Definition at line 67 of file qgsaggregatecalculator.h.

Constructor & Destructor Documentation

◆ QgsAggregateCalculator()

QgsAggregateCalculator::QgsAggregateCalculator ( const QgsVectorLayer * layer )

Constructor for QgsAggregateCalculator.

Parameters

layer vector layer to calculate aggregate from

Definition at line 28 of file qgsaggregatecalculator.cpp.

Member Function Documentation

◆ aggregates()

QList< QgsAggregateCalculator::AggregateInfo > QgsAggregateCalculator::aggregates ( )

static

Structured information for available aggregates.

Since: QGIS 3.2

Definition at line 298 of file qgsaggregatecalculator.cpp.

◆ calculate()

QVariant QgsAggregateCalculator::calculate	(	QgsAggregateCalculator::Aggregate	aggregate,
		const QString &	fieldOrExpression,
		QgsExpressionContext *	context = `nullptr`,
		bool *	ok = `nullptr`,
		QgsFeedback *	feedback = `nullptr`
	)		const

Calculates the value of an aggregate.

Parameters

aggregate	aggregate to calculate
fieldOrExpression	source field or expression to use as basis for aggregated values. If an expression is used, then the context parameter must be set.
context	expression context for evaluating expressions
ok	if specified, will be set to `true` if aggregate calculation was successful. If ok is `false` then lastError() can be used to retrieve a descriptive error message.
feedback	optional feedback argument for early cancellation (since QGIS 3.22). If set, this will take precedence over any feedback object set on the expression context.

Returns: calculated aggregate value

Definition at line 52 of file qgsaggregatecalculator.cpp.

◆ delimiter()

QString QgsAggregateCalculator::delimiter ( ) const

inline

Returns the delimiter used for joining values with the StringConcatenate aggregate.

See also: setDelimiter()

Definition at line 175 of file qgsaggregatecalculator.h.

◆ displayName()

QString QgsAggregateCalculator::displayName ( Aggregate aggregate )

static

Returns the friendly display name for a aggregate.

Since: QGIS 3.22

Definition at line 246 of file qgsaggregatecalculator.cpp.

◆ filter()

QString QgsAggregateCalculator::filter ( ) const

inline

Returns the filter which limits the features used during the aggregate calculation.

See also: setFilter()

Definition at line 162 of file qgsaggregatecalculator.h.

◆ lastError()

QString QgsAggregateCalculator::lastError ( ) const

inline

Returns the last error encountered during the aggregate calculation.

Since: QGIS 3.22

Definition at line 130 of file qgsaggregatecalculator.h.

◆ layer()

const QgsVectorLayer * QgsAggregateCalculator::layer ( ) const

Returns the associated vector layer.

Definition at line 34 of file qgsaggregatecalculator.cpp.

◆ setDelimiter()

void QgsAggregateCalculator::setDelimiter ( const QString & delimiter )

inline

Sets the delimiter to use for joining values with the StringConcatenate aggregate.

Parameters

delimiter string delimiter

See also: delimiter()

Definition at line 169 of file qgsaggregatecalculator.h.

◆ setFidsFilter()

void QgsAggregateCalculator::setFidsFilter ( const QgsFeatureIds & fids )

Sets a filter to limit the features used during the aggregate calculation.

If an expression filter is set, it will override this filter.

Parameters

fids	feature ids for feature filtering, and empty list will return no features.

See also: filter()

Definition at line 46 of file qgsaggregatecalculator.cpp.

◆ setFilter()

void QgsAggregateCalculator::setFilter ( const QString & filterExpression )

inline

Sets a filter to limit the features used during the aggregate calculation.

Parameters

filterExpression expression for filtering features, or empty string to remove filter

See also: filter()

Definition at line 148 of file qgsaggregatecalculator.h.

◆ setParameters()

void QgsAggregateCalculator::setParameters ( const AggregateParameters & parameters )

Sets all aggregate parameters from a parameter bundle.

Parameters

parameters aggregate parameters

Definition at line 39 of file qgsaggregatecalculator.cpp.

◆ stringToAggregate()

QgsAggregateCalculator::Aggregate QgsAggregateCalculator::stringToAggregate	(	const QString &	string,
		bool *	ok = `nullptr`
	)

static

Converts a string to a aggregate type.

Parameters

string	string to convert
ok	if specified, will be set to `true` if conversion was successful

Returns: aggregate type

Definition at line 188 of file qgsaggregatecalculator.cpp.

The documentation for this class was generated from the following files:

/build/qgis-3.22.4+99unstable/src/core/qgsaggregatecalculator.h
/build/qgis-3.22.4+99unstable/src/core/qgsaggregatecalculator.cpp

Classes

Public Types

Public Member Functions

Static Public Member Functions

Detailed Description

Member Enumeration Documentation

◆ Aggregate

Constructor & Destructor Documentation

◆ QgsAggregateCalculator()

Member Function Documentation

◆ aggregates()

◆ calculate()

◆ delimiter()

◆ displayName()

◆ filter()

◆ lastError()

◆ layer()

◆ setDelimiter()

◆ setFidsFilter()

◆ setFilter()

◆ setParameters()

◆ stringToAggregate()