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2a326ef8ad
This feature adds a 'collect' aggregation method resulting in a single multipart geometry from a list of geometries. This is exposed in the expression engine via the existing aggregate() function, as well as a new collect() function.
116 lines
4.6 KiB
Plaintext
116 lines
4.6 KiB
Plaintext
/** \ingroup core
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* \class QgsAggregateCalculator
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* \brief Utility class for calculating aggregates for a field (or expression) over the features
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* from a vector layer. It is recommended that QgsVectorLayer::aggregate() is used rather then
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* directly using this class, as the QgsVectorLayer method can handle delegating aggregate calculation
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* to a data provider for remote calculation.
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* \note added in QGIS 2.16
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*/
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class QgsAggregateCalculator
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{
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%TypeHeaderCode
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#include <qgsaggregatecalculator.h>
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%End
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public:
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//! Available aggregates to calculate. Not all aggregates are available for all field
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//! types.
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enum Aggregate
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{
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Count, //!< Count
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CountDistinct, //!< Number of distinct values
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CountMissing, //!< Number of missing (null) values
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Min, //!< Min of values
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Max, //!< Max of values
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Sum, //!< Sum of values
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Mean, //!< Mean of values (numeric fields only)
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Median, //!< Median of values (numeric fields only)
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StDev, //!< Standard deviation of values (numeric fields only)
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StDevSample, //!< Sample standard deviation of values (numeric fields only)
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Range, //!< Range of values (max - min) (numeric and datetime fields only)
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Minority, //!< Minority of values (numeric fields only)
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Majority, //!< Majority of values (numeric fields only)
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FirstQuartile, //!< First quartile (numeric fields only)
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ThirdQuartile, //!< Third quartile (numeric fields only)
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InterQuartileRange, //!< Inter quartile range (IQR) (numeric fields only)
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StringMinimumLength, //!< Minimum length of string (string fields only)
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StringMaximumLength, //!< Maximum length of string (string fields only)
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StringConcatenate, //! Concatenate values with a joining string (string fields only). Specify the delimiter using setDelimiter().
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GeometryCollect, //! Create a multipart geometry from aggregated geometries
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};
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//! A bundle of parameters controlling aggregate calculation
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struct AggregateParameters
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{
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/** Optional filter for calculating aggregate over a subset of features, or an
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* empty string to use all features.
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* @see QgsAggregateCalculator::setFilter()
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* @see QgsAggregateCalculator::filter()
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*/
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QString filter;
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/** Delimiter to use for joining values with the StringConcatenate aggregate.
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* @see QgsAggregateCalculator::setDelimiter()
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* @see QgsAggregateCalculator::delimiter()
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*/
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QString delimiter;
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};
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/** Constructor for QgsAggregateCalculator.
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* @param layer vector layer to calculate aggregate from
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*/
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QgsAggregateCalculator( const QgsVectorLayer* layer );
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/** Returns the associated vector layer.
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*/
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const QgsVectorLayer* layer() const;
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/** Sets all aggregate parameters from a parameter bundle.
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* @param parameters aggregate parameters
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*/
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void setParameters( const AggregateParameters& parameters );
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/** Sets a filter to limit the features used during the aggregate calculation.
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* @param filterExpression expression for filtering features, or empty string to remove filter
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* @see filter()
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*/
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void setFilter( const QString& filterExpression );
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/** Returns the filter which limits the features used during the aggregate calculation.
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* @see setFilter()
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*/
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QString filter() const;
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/** Sets the delimiter to use for joining values with the StringConcatenate aggregate.
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* @param delimiter string delimiter
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* @see delimiter()
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*/
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void setDelimiter( const QString& delimiter );
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/** Returns the delimiter used for joining values with the StringConcatenate aggregate.
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* @see setDelimiter()
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*/
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QString delimiter() const;
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/** Calculates the value of an aggregate.
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* @param aggregate aggregate to calculate
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* @param fieldOrExpression source field or expression to use as basis for aggregated values.
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* If an expression is used, then the context parameter must be set.
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* @param context expression context for evaluating expressions
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* @param ok if specified, will be set to true if aggregate calculation was successful
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* @returns calculated aggregate value
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*/
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QVariant calculate( Aggregate aggregate, const QString& fieldOrExpression,
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QgsExpressionContext* context = nullptr, bool* ok = nullptr ) const;
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/** Converts a string to a aggregate type.
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* @param string string to convert
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* @param ok if specified, will be set to true if conversion was successful
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* @returns aggregate type
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*/
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static Aggregate stringToAggregate( const QString& string, bool* ok = nullptr );
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};
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