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New utility class QgsAggregateCalculator, simplifies calculating

aggregates from vector layer fields and expressions
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nyalldawson committed May 17, 2016
1 parent 1c45b94 commit 50e41c8133cc312684b6f7a8b812bb3e9e06d5c1
@@ -21,6 +21,7 @@
%Include qgsapplication.sip
%Include qgsaction.sip
%Include qgsactionmanager.sip
%Include qgsaggregatecalculator.sip
%Include qgsattributeaction.sip
%Include qgsattributetableconfig.sip
%Include qgsbrowsermodel.sip
@@ -0,0 +1,72 @@
/** \ingroup core
* \class QgsAggregateCalculator
* \brief Utility class for calculating aggregates for a field (or expression) over the features
* from a vector layer.
* \note added in QGIS 2.16
class QgsAggregateCalculator

#include <qgsaggregatecalculator.h>


//! Available aggregates to calculate. Not all aggregates are available for all field
//! types.
enum Aggregate
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)

/** Constructor for QgsAggregateCalculator.
* @param layer vector layer to calculate aggregate from
QgsAggregateCalculator( QgsVectorLayer* layer );

/** Returns the associated vector layer.
QgsVectorLayer* layer() const;

/** Sets a filter to limit the features used during the aggregate calculation.
* @param filterExpression expression for filtering features, or empty string to remove filter
* @see filter()
void setFilter( const QString& filterExpression );

/** Returns the filter which limits the features used during the aggregate calculation.
* @see setFilter()
QString filter() const;

/** Calculates the value of an aggregate.
* @param aggregate aggregate to calculate
* @param fieldOrExpression source field or expression to use as basis for aggregated values.
* If an expression is used, then the context parameter must be set.
* @param context expression context for evaluating expressions
* @param ok if specified, will be set to true if aggregate calculation was successful
* @returns calculated aggregate value
QVariant calculate( Aggregate aggregate, const QString& fieldOrExpression,
QgsExpressionContext* context = nullptr, bool* ok = nullptr ) const;

@@ -79,6 +79,7 @@ SET(QGIS_CORE_SRCS
@@ -597,6 +598,7 @@ SET(QGIS_CORE_HDRS


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