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fee8734596
This deprecates forcing a return value for ArrayAgg, JSONBAgg, and StringAgg when there are no rows in the query. Now that we have a ``default`` argument for aggregates, we want to revert to returning the default of ``None`` which most aggregate functions return and leave it up to the user to decide what they want to be returned by default.
330 lines
10 KiB
Plaintext
330 lines
10 KiB
Plaintext
=========================================
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PostgreSQL specific aggregation functions
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=========================================
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.. module:: django.contrib.postgres.aggregates
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:synopsis: PostgreSQL specific aggregation functions
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These functions are available from the ``django.contrib.postgres.aggregates``
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module. They are described in more detail in the `PostgreSQL docs
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<https://www.postgresql.org/docs/current/functions-aggregate.html>`_.
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.. note::
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All functions come without default aliases, so you must explicitly provide
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one. For example::
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>>> SomeModel.objects.aggregate(arr=ArrayAgg('somefield'))
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{'arr': [0, 1, 2]}
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.. admonition:: Common aggregate options
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All aggregates have the :ref:`filter <aggregate-filter>` keyword argument
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and most also have the :ref:`default <aggregate-default>` keyword argument.
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General-purpose aggregation functions
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=====================================
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``ArrayAgg``
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------------
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.. class:: ArrayAgg(expression, distinct=False, filter=None, default=None, ordering=(), **extra)
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Returns a list of values, including nulls, concatenated into an array, or
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``default`` if there are no values.
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.. attribute:: distinct
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An optional boolean argument that determines if array values
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will be distinct. Defaults to ``False``.
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.. attribute:: ordering
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An optional string of a field name (with an optional ``"-"`` prefix
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which indicates descending order) or an expression (or a tuple or list
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of strings and/or expressions) that specifies the ordering of the
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elements in the result list.
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Examples::
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'some_field'
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'-some_field'
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from django.db.models import F
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F('some_field').desc()
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.. deprecated:: 4.0
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If there are no rows and ``default`` is not provided, ``ArrayAgg``
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returns an empty list instead of ``None``. This behavior is deprecated
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and will be removed in Django 5.0. If you need it, explicitly set
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``default`` to ``Value([])``.
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``BitAnd``
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----------
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.. class:: BitAnd(expression, filter=None, default=None, **extra)
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Returns an ``int`` of the bitwise ``AND`` of all non-null input values, or
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``default`` if all values are null.
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``BitOr``
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---------
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.. class:: BitOr(expression, filter=None, default=None, **extra)
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Returns an ``int`` of the bitwise ``OR`` of all non-null input values, or
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``default`` if all values are null.
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``BoolAnd``
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-----------
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.. class:: BoolAnd(expression, filter=None, default=None, **extra)
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Returns ``True``, if all input values are true, ``default`` if all values
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are null or if there are no values, otherwise ``False``.
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Usage example::
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class Comment(models.Model):
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body = models.TextField()
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published = models.BooleanField()
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rank = models.IntegerField()
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>>> from django.db.models import Q
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>>> from django.contrib.postgres.aggregates import BoolAnd
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>>> Comment.objects.aggregate(booland=BoolAnd('published'))
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{'booland': False}
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>>> Comment.objects.aggregate(booland=BoolAnd(Q(rank__lt=100)))
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{'booland': True}
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``BoolOr``
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----------
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.. class:: BoolOr(expression, filter=None, default=None, **extra)
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Returns ``True`` if at least one input value is true, ``default`` if all
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values are null or if there are no values, otherwise ``False``.
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Usage example::
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class Comment(models.Model):
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body = models.TextField()
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published = models.BooleanField()
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rank = models.IntegerField()
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>>> from django.db.models import Q
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>>> from django.contrib.postgres.aggregates import BoolOr
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>>> Comment.objects.aggregate(boolor=BoolOr('published'))
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{'boolor': True}
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>>> Comment.objects.aggregate(boolor=BoolOr(Q(rank__gt=2)))
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{'boolor': False}
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``JSONBAgg``
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------------
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.. class:: JSONBAgg(expressions, distinct=False, filter=None, default=None, ordering=(), **extra)
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Returns the input values as a ``JSON`` array, or ``default`` if there are
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no values.
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.. attribute:: distinct
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.. versionadded:: 3.2
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An optional boolean argument that determines if array values will be
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distinct. Defaults to ``False``.
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.. attribute:: ordering
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.. versionadded:: 3.2
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An optional string of a field name (with an optional ``"-"`` prefix
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which indicates descending order) or an expression (or a tuple or list
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of strings and/or expressions) that specifies the ordering of the
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elements in the result list.
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Examples are the same as for :attr:`ArrayAgg.ordering`.
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.. deprecated:: 4.0
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If there are no rows and ``default`` is not provided, ``JSONBAgg``
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returns an empty list instead of ``None``. This behavior is deprecated
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and will be removed in Django 5.0. If you need it, explicitly set
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``default`` to ``Value('[]')``.
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``StringAgg``
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-------------
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.. class:: StringAgg(expression, delimiter, distinct=False, filter=None, default=None, ordering=())
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Returns the input values concatenated into a string, separated by
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the ``delimiter`` string, or ``default`` if there are no values.
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.. attribute:: delimiter
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Required argument. Needs to be a string.
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.. attribute:: distinct
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An optional boolean argument that determines if concatenated values
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will be distinct. Defaults to ``False``.
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.. attribute:: ordering
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An optional string of a field name (with an optional ``"-"`` prefix
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which indicates descending order) or an expression (or a tuple or list
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of strings and/or expressions) that specifies the ordering of the
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elements in the result string.
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Examples are the same as for :attr:`ArrayAgg.ordering`.
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.. deprecated:: 4.0
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If there are no rows and ``default`` is not provided, ``StringAgg``
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returns an empty string instead of ``None``. This behavior is
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deprecated and will be removed in Django 5.0. If you need it,
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explicitly set ``default`` to ``Value('')``.
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Aggregate functions for statistics
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==================================
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``y`` and ``x``
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---------------
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The arguments ``y`` and ``x`` for all these functions can be the name of a
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field or an expression returning a numeric data. Both are required.
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``Corr``
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--------
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.. class:: Corr(y, x, filter=None, default=None)
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Returns the correlation coefficient as a ``float``, or ``default`` if there
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aren't any matching rows.
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``CovarPop``
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------------
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.. class:: CovarPop(y, x, sample=False, filter=None, default=None)
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Returns the population covariance as a ``float``, or ``default`` if there
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aren't any matching rows.
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Has one optional argument:
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.. attribute:: sample
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By default ``CovarPop`` returns the general population covariance.
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However, if ``sample=True``, the return value will be the sample
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population covariance.
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``RegrAvgX``
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------------
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.. class:: RegrAvgX(y, x, filter=None, default=None)
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Returns the average of the independent variable (``sum(x)/N``) as a
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``float``, or ``default`` if there aren't any matching rows.
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``RegrAvgY``
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------------
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.. class:: RegrAvgY(y, x, filter=None, default=None)
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Returns the average of the dependent variable (``sum(y)/N``) as a
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``float``, or ``default`` if there aren't any matching rows.
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``RegrCount``
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-------------
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.. class:: RegrCount(y, x, filter=None)
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Returns an ``int`` of the number of input rows in which both expressions
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are not null.
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.. note::
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The ``default`` argument is not supported.
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``RegrIntercept``
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-----------------
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.. class:: RegrIntercept(y, x, filter=None, default=None)
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Returns the y-intercept of the least-squares-fit linear equation determined
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by the ``(x, y)`` pairs as a ``float``, or ``default`` if there aren't any
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matching rows.
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``RegrR2``
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----------
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.. class:: RegrR2(y, x, filter=None, default=None)
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Returns the square of the correlation coefficient as a ``float``, or
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``default`` if there aren't any matching rows.
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``RegrSlope``
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-------------
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.. class:: RegrSlope(y, x, filter=None, default=None)
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Returns the slope of the least-squares-fit linear equation determined
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by the ``(x, y)`` pairs as a ``float``, or ``default`` if there aren't any
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matching rows.
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``RegrSXX``
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-----------
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.. class:: RegrSXX(y, x, filter=None, default=None)
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Returns ``sum(x^2) - sum(x)^2/N`` ("sum of squares" of the independent
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variable) as a ``float``, or ``default`` if there aren't any matching rows.
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``RegrSXY``
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-----------
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.. class:: RegrSXY(y, x, filter=None, default=None)
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Returns ``sum(x*y) - sum(x) * sum(y)/N`` ("sum of products" of independent
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times dependent variable) as a ``float``, or ``default`` if there aren't
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any matching rows.
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``RegrSYY``
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-----------
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.. class:: RegrSYY(y, x, filter=None, default=None)
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Returns ``sum(y^2) - sum(y)^2/N`` ("sum of squares" of the dependent
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variable) as a ``float``, or ``default`` if there aren't any matching rows.
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Usage examples
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==============
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We will use this example table::
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| FIELD1 | FIELD2 | FIELD3 |
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|--------|--------|--------|
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| foo | 1 | 13 |
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| bar | 2 | (null) |
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| test | 3 | 13 |
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Here's some examples of some of the general-purpose aggregation functions::
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>>> TestModel.objects.aggregate(result=StringAgg('field1', delimiter=';'))
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{'result': 'foo;bar;test'}
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>>> TestModel.objects.aggregate(result=ArrayAgg('field2'))
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{'result': [1, 2, 3]}
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>>> TestModel.objects.aggregate(result=ArrayAgg('field1'))
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{'result': ['foo', 'bar', 'test']}
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The next example shows the usage of statistical aggregate functions. The
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underlying math will be not described (you can read about this, for example, at
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`wikipedia <https://en.wikipedia.org/wiki/Regression_analysis>`_)::
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>>> TestModel.objects.aggregate(count=RegrCount(y='field3', x='field2'))
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{'count': 2}
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>>> TestModel.objects.aggregate(avgx=RegrAvgX(y='field3', x='field2'),
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... avgy=RegrAvgY(y='field3', x='field2'))
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{'avgx': 2, 'avgy': 13}
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