QgsAggregateCalculator Class Reference

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 }
	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) 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...
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	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 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 42 of file qgsaggregatecalculator.h.

Member Enumeration Documentation

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 (numeric fields only)
Majority	Majority of values (numeric fields only)
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
GeometryCollect	Concatenate values with a joining string (string fields only). Specify the delimiter using setDelimiter().
ArrayAggregate	Create a multipart geometry from aggregated geometries. Create an array of values

Definition at line 62 of file qgsaggregatecalculator.h.

Constructor & Destructor Documentation

QgsAggregateCalculator::QgsAggregateCalculator

(

const QgsVectorLayer *

layer

)

Constructor for QgsAggregateCalculator.

Parameters

layer

vector layer to calculate aggregate from

Definition at line 27 of file qgsaggregatecalculator.cpp.

Member Function Documentation

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

static

Structured information for available aggregates.

Since

QGIS 3.2

Definition at line 177 of file qgsaggregatecalculator.cpp.

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

Returns

calculated aggregate value

Definition at line 44 of file qgsaggregatecalculator.cpp.

QString QgsAggregateCalculator::delimiter ( ) const

inline

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

See also

setDelimiter()

Definition at line 148 of file qgsaggregatecalculator.h.

QString QgsAggregateCalculator::filter ( ) const

inline

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

See also

setFilter()

Definition at line 135 of file qgsaggregatecalculator.h.

const QgsVectorLayer * QgsAggregateCalculator::layer

(

)

const

Returns the associated vector layer.

Definition at line 33 of file qgsaggregatecalculator.cpp.

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 142 of file qgsaggregatecalculator.h.

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 129 of file qgsaggregatecalculator.h.

void QgsAggregateCalculator::setParameters

(

const AggregateParameters &

parameters

)

Sets all aggregate parameters from a parameter bundle.

Parameters

parameters

aggregate parameters

Definition at line 38 of file qgsaggregatecalculator.cpp.

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 121 of file qgsaggregatecalculator.cpp.

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

• /build/qgis-3.4.15+24xenial/src/core/qgsaggregatecalculator.h
• /build/qgis-3.4.15+24xenial/src/core/qgsaggregatecalculator.cpp