Class: QgsAggregateCalculator¶

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

Note

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.

Enums

Aggregate

Available aggregates to calculate.

Methods

`calculate`	Calculates the value of an aggregate.
`delimiter`	Returns the delimiter used for joining values with the StringConcatenate aggregate.
`filter`	Returns the filter which limits the features used during the aggregate calculation.
`lastError`	Returns the last error encountered during the aggregate calculation.
`layer`	Returns the associated vector layer.
`setDelimiter`	Sets the delimiter to use for joining values with the StringConcatenate aggregate.
`setFidsFilter`	Sets a filter to limit the features used during the aggregate calculation.
`setFilter`	Sets a filter to limit the features used during the aggregate calculation.
`setParameters`	Sets all aggregate parameters from a parameter bundle.

Static Methods

`aggregates`	Structured information for available aggregates.
`displayName`	Returns the friendly display name for a aggregate.
`stringToAggregate`	Converts a string to a aggregate type.

class qgis.core.QgsAggregateCalculator[source]¶

Bases: object

__init__(layer: QgsVectorLayer | None)

Constructor for QgsAggregateCalculator.

Parameters:: layer (Optional[QgsVectorLayer]) – vector layer to calculate aggregate from

__init__(a0: QgsAggregateCalculator)

Parameters:: a0 (QgsAggregateCalculator)

class Aggregate(*values)¶

Bases: IntEnum

Available aggregates to calculate. Not all aggregates are available for all field types.

Added in version 3.36..

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().

class AggregateInfo¶

Bases: object

Structured information about the available aggregates.

function¶: The expression function

name¶: A translated, human readable name

supportedTypes¶: This aggregate function can only be used with these datatypes

class AggregateParameters¶

Bases: object

A bundle of parameters controlling aggregate calculation

delimiter¶: Delimiter to use for joining values with the StringConcatenate aggregate.

See also

QgsAggregateCalculator.setDelimiter()

See also

QgsAggregateCalculator.delimiter()

filter¶: Optional filter for calculating aggregate over a subset of features, or an empty string to use all features.

See also

QgsAggregateCalculator.setFilter()

See also

QgsAggregateCalculator.filter()

orderBy¶: Optional order by clauses.

Added in version 3.8.

static aggregates() → List[QgsAggregateCalculator.AggregateInfo]¶

Structured information for available aggregates.

Added in version 3.2.

Return type:: List[QgsAggregateCalculator.AggregateInfo]

calculate(self, aggregate: Qgis.Aggregate, fieldOrExpression: str | None, context: QgsExpressionContext | None = None, feedback: QgsFeedback | None = None)[source]¶

Calculates the value of an aggregate.

Parameters:

aggregate (Qgis.Aggregate) – aggregate to calculate
fieldOrExpression (Optional[str]) – source field or expression to use as basis for aggregated values. If an expression is used, then the context parameter must be set.
context (Optional[QgsExpressionContext] = None) – 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[QgsFeedback] = None) -> (Any) – 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

delimiter(self) → str[source]¶

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

See also

setDelimiter()

Return type:: str

static displayName(aggregate: Qgis.Aggregate) → str[source]¶

Returns the friendly display name for a aggregate.

Added in version 3.22.

Parameters:: aggregate (Qgis.Aggregate)
Return type:: str

filter(self) → str[source]¶

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

See also

setFilter()

Return type:: str

lastError(self) → str[source]¶

Returns the last error encountered during the aggregate calculation.

Added in version 3.22.

Return type:: str

layer(self) → QgsVectorLayer | None[source]¶

Returns the associated vector layer.

Return type:: Optional[QgsVectorLayer]

setDelimiter(self, delimiter: str | None)[source]¶

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

Parameters:: delimiter (Optional[str]) – string delimiter

See also

delimiter()

setFidsFilter(self, fids: Any)[source]¶

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 (Any) – feature ids for feature filtering, and empty list will return no features.

See also

filter()

setFilter(self, filterExpression: str | None)[source]¶

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

Parameters:: filterExpression (Optional[str]) – expression for filtering features, or empty string to remove filter

See also

filter()

setParameters(self, parameters: QgsAggregateCalculator.AggregateParameters)[source]¶

Sets all aggregate parameters from a parameter bundle.

Parameters:: parameters (QgsAggregateCalculator.AggregateParameters) – aggregate parameters

static stringToAggregate(string: str | None)[source]¶

Converts a string to a aggregate type.

Parameters:

string (Optional[str]) -> (Qgis.Aggregate) – string to convert
ok – if specified, will be set to True if conversion was successful

Returns:

aggregate type