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307aabd66a
This commit adds a number of different forms of aggregates to
the expression engine.
1. Aggregates within the current layer, eg sum("passengers")
Supports sub expressions (ie sum("passengers"/2) ), group by
( sum("passengers", group_by:="line_segment") ), and optional
filters ( sum("passengers", filter:= "station_class" > 3 ) )
2. Relational aggregates, which calculate an aggregate over
all matching child features from a relation, eg
relation_aggregate( 'my_relation', 'mean', "some_child_field" )
3. A summary aggregate function, for calculating aggregates
on other layers. Eg aggregate('rail_station_layer','sum',"passengers")
The summary aggregate function supports an optional filter,
making it possible to calculate things like:
aggregate('rail_stations','sum',"passengers",
intersects(@atlas_geometry, $geometry ) )
for calculating the total number of passengers for the stations
inside the current atlas feature
In all cases the calculations are cached inside the expression
context, so they only need to be calculated once for each
set of expression evaluations.
Sponsored by Kanton of Zug, Switzerland
215 lines
7.3 KiB
Plaintext
215 lines
7.3 KiB
Plaintext
/** \ingroup core
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* \class QgsStatisticalSummary
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* \brief Calculator for summary statistics for a list of doubles.
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*
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* Statistics are calculated by calling @link calculate @endlink and passing a list of doubles. The
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* individual statistics can then be retrieved using the associated methods. Note that not all statistics
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* are calculated by default. Statistics which require slower computations are only calculated by
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* specifying the statistic in the constructor or via @link setStatistics @endlink.
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*
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* \note Added in version 2.9
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*/
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class QgsStatisticalSummary
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{
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%TypeHeaderCode
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#include <qgsstatisticalsummary.h>
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%End
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public:
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//! Enumeration of flags that specify statistics to be calculated
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enum Statistic
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{
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Count, //!< Count
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CountMissing, //!< Number of missing (null) values
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Sum, //!< Sum of values
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Mean, //!< Mean of values
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Median, //!< Median of values
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StDev, //!< Standard deviation of values
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StDevSample, //!< Sample standard deviation of values
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Min, //!< Min of values
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Max, //!< Max of values
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Range, //!< Range of values (max - min)
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Minority, //!< Minority of values
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Majority, //!< Majority of values
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Variety, //!< Variety (count of distinct) values
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FirstQuartile, //!< First quartile
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ThirdQuartile, //!< Third quartile
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InterQuartileRange, //!< Inter quartile range (IQR)
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All
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};
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typedef QFlags<QgsStatisticalSummary::Statistic> Statistics;
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/** Constructor for QgsStatisticalSummary
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* @param stats flags for statistics to calculate
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*/
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QgsStatisticalSummary( const QgsStatisticalSummary::Statistics& stats = QgsStatisticalSummary::All );
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virtual ~QgsStatisticalSummary();
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/** Returns flags which specify which statistics will be calculated. Some statistics
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* are always calculated (eg sum, min and max).
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* @see setStatistics
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*/
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QgsStatisticalSummary::Statistics statistics() const;
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/** Sets flags which specify which statistics will be calculated. Some statistics
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* are always calculated (eg sum, min and max).
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* @param stats flags for statistics to calculate
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* @see statistics
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*/
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void setStatistics( const QgsStatisticalSummary::Statistics& stats );
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/** Resets the calculated values
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*/
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void reset();
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/** Calculates summary statistics for a list of values
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* @param values list of doubles
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*/
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void calculate( const QList<double>& values );
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/** Adds a single value to the statistics calculation. Calling this method
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* allows values to be added to the calculation one at a time. For large
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* quantities of values this may be more efficient then first adding all the
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* values to a list and calling calculate().
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* @param value value to add
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* @note call reset() before adding the first value using this method
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* to clear the results from any previous calculations
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* @note finalize() must be called after adding the final value and before
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* retrieving calculated statistics.
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* @see calculate()
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* @see addVariant()
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* @see finalize()
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* @note added in QGIS 2.16
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*/
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void addValue( double value );
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/** Adds a single value to the statistics calculation. Calling this method
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* allows values to be added to the calculation one at a time. For large
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* quantities of values this may be more efficient then first adding all the
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* values to a list and calling calculate().
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* @param value variant containing to add. Non-numeric values are treated as null.
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* @note call reset() before adding the first value using this method
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* to clear the results from any previous calculations
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* @note finalize() must be called after adding the final value and before
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* retrieving calculated statistics.
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* @see addValue()
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* @see calculate()
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* @see finalize()
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* @note added in QGIS 2.16
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*/
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void addVariant( const QVariant& value );
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/** Must be called after adding all values with addValues() and before retrieving
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* any calculated statistics.
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* @see addValue()
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* @see addVariant()
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* @note added in QGIS 2.16
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*/
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void finalize();
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/** Returns the value of a specified statistic
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* @param stat statistic to return
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* @returns calculated value of statistic
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*/
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double statistic( Statistic stat ) const;
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/** Returns calculated count of values
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*/
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int count() const;
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/** Returns the number of missing (null) values
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* @note added in QGIS 2.16
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*/
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int countMissing() const;
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/** Returns calculated sum of values
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*/
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double sum() const;
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/** Returns calculated mean of values
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*/
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double mean() const;
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/** Returns calculated median of values. This is only calculated if Statistic::Median has
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* been specified in the constructor or via setStatistics.
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*/
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double median() const;
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/** Returns calculated minimum from values.
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*/
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double min() const;
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/** Returns calculated maximum from values.
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*/
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double max() const;
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/** Returns calculated range (difference between maximum and minimum values).
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*/
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double range() const;
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/** Returns population standard deviation. This is only calculated if Statistic::StDev has
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* been specified in the constructor or via setStatistics.
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* @see sampleStDev
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*/
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double stDev() const;
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/** Returns sample standard deviation. This is only calculated if Statistic::StDev has
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* been specified in the constructor or via setStatistics.
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* @see stDev
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*/
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double sampleStDev() const;
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/** Returns variety of values. The variety is the count of unique values from the list.
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* This is only calculated if Statistic::Variety has been specified in the constructor
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* or via setStatistics.
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*/
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int variety() const;
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/** Returns minority of values. The minority is the value with least occurances in the list
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* This is only calculated if Statistic::Minority has been specified in the constructor
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* or via setStatistics.
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* @see majority
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*/
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double minority() const;
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/** Returns majority of values. The majority is the value with most occurances in the list
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* This is only calculated if Statistic::Majority has been specified in the constructor
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* or via setStatistics.
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* @see minority
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*/
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double majority() const;
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/** Returns the first quartile of the values. The quartile is calculated using the
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* "Tukey's hinges" method.
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* @see thirdQuartile
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* @see interQuartileRange
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*/
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double firstQuartile() const;
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/** Returns the third quartile of the values. The quartile is calculated using the
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* "Tukey's hinges" method.
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* @see firstQuartile
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* @see interQuartileRange
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*/
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double thirdQuartile() const;
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/** Returns the inter quartile range of the values. The quartiles are calculated using the
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* "Tukey's hinges" method.
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* @see firstQuartile
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* @see thirdQuartile
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*/
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double interQuartileRange() const;
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/** Returns the friendly display name for a statistic
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* @param statistic statistic to return name for
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*/
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static QString displayName( Statistic statistic );
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};
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QFlags<QgsStatisticalSummary::Statistic> operator|(QgsStatisticalSummary::Statistic f1, QFlags<QgsStatisticalSummary::Statistic> f2);
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