========================================= PostgreSQL specific aggregation functions ========================================= .. module:: django.contrib.postgres.aggregates :synopsis: PostgreSQL specific aggregation functions .. versionadded:: 1.9 These functions are described in more detail in the `PostgreSQL docs `_. .. note:: All functions come without default aliases, so you must explicitly provide one. For example:: >>> SomeModel.objects.aggregate(arr=ArrayAgg('somefield')) {'arr': [0, 1, 2]} General-purpose aggregation functions ===================================== ``ArrayAgg`` ------------ .. class:: ArrayAgg(expression, **extra) Returns a list of values, including nulls, concatenated into an array. ``BitAnd`` ---------- .. class:: BitAnd(expression, **extra) Returns an ``int`` of the bitwise ``AND`` of all non-null input values, or ``None`` if all values are null. ``BitOr`` --------- .. class:: BitOr(expression, **extra) Returns an ``int`` of the bitwise ``OR`` of all non-null input values, or ``None`` if all values are null. ``BoolAnd`` ----------- .. class:: BoolAnd(expression, **extra) Returns ``True``, if all input values are true, ``None`` if all values are null or if there are no values, otherwise ``False`` . ``BoolOr`` ---------- .. class:: BoolOr(expression, **extra) Returns ``True`` if at least one input value is true, ``None`` if all values are null or if there are no values, otherwise ``False``. ``StringAgg`` ------------- .. class:: StringAgg(expression, delimiter) Returns the input values concatenated into a string, separated by the ``delimiter`` string. .. attribute:: delimiter Required argument. Needs to be a string. Aggregate functions for statistics ================================== ``y`` and ``x`` --------------- The arguments ``y`` and ``x`` for all these functions can be the name of a field or an expression returning a numeric data. Both are required. ``Corr`` -------- .. class:: Corr(y, x) Returns the correlation coefficient as a ``float``, or ``None`` if there aren't any matching rows. ``CovarPop`` ------------ .. class:: CovarPop(y, x, sample=False) Returns the population covariance as a ``float``, or ``None`` if there aren't any matching rows. Has one optional argument: .. attribute:: sample By default ``CovarPop`` returns the general population covariance. However, if ``sample=True``, the return value will be the sample population covariance. ``RegrAvgX`` ------------ .. class:: RegrAvgX(y, x) Returns the average of the independent variable (``sum(x)/N``) as a ``float``, or ``None`` if there aren't any matching rows. ``RegrAvgY`` ------------ .. class:: RegrAvgY(y, x) Returns the average of the dependent variable (``sum(y)/N``) as a ``float``, or ``None`` if there aren't any matching rows. ``RegrCount`` ------------- .. class:: RegrCount(y, x) Returns an ``int`` of the number of input rows in which both expressions are not null. ``RegrIntercept`` ----------------- .. class:: RegrIntercept(y, x) Returns the y-intercept of the least-squares-fit linear equation determined by the ``(x, y)`` pairs as a ``float``, or ``None`` if there aren't any matching rows. ``RegrR2`` ---------- .. class:: RegrR2(y, x) Returns the square of the correlation coefficient as a ``float``, or ``None`` if there aren't any matching rows. ``RegrSlope`` ------------- .. class:: RegrSlope(y, x) Returns the slope of the least-squares-fit linear equation determined by the ``(x, y)`` pairs as a ``float``, or ``None`` if there aren't any matching rows. ``RegrSXX`` ----------- .. class:: RegrSXX(y, x) Returns ``sum(x^2) - sum(x)^2/N`` ("sum of squares" of the independent variable) as a ``float``, or ``None`` if there aren't any matching rows. ``RegrSXY`` ----------- .. class:: RegrSXY(y, x) Returns ``sum(x*y) - sum(x) * sum(y)/N`` ("sum of products" of independent times dependent variable) as a ``float``, or ``None`` if there aren't any matching rows. ``RegrSYY`` ----------- .. class:: RegrSYY(y, x) Returns ``sum(y^2) - sum(y)^2/N`` ("sum of squares" of the dependent variable) as a ``float``, or ``None`` if there aren't any matching rows. Usage examples ============== We will use this example table:: | FIELD1 | FIELD2 | FIELD3 | |--------|--------|--------| | foo | 1 | 13 | | bar | 2 | (null) | | test | 3 | 13 | Here's some examples of some of the general-purpose aggregation functions:: >>> TestModel.objects.aggregate(result=StringAgg('field1', delimiter=';')) {'result': 'foo;bar;test'} >>> TestModel.objects.aggregate(result=ArrayAgg('field2')) {'result': [1, 2, 3]} >>> TestModel.objects.aggregate(result=ArrayAgg('field1')) {'result': ['foo', 'bar', 'test']} The next example shows the usage of statistical aggregate functions. The underlying math will be not described (you can read about this, for example, at `wikipedia `_):: >>> TestModel.objects.aggregate(count=RegrCount(y='field3', x='field2')) {'count': 2} >>> TestModel.objects.aggregate(avgx=RegrAvgX(y='field3', x='field2'), ... avgy=RegrAvgY(y='field3', x='field2')) {'avgx': 2, 'avgy': 13}