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394 lines
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394 lines
12 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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.. code-block:: pycon
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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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.. versionchanged:: 5.0
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In older versions, if there are no rows and ``default`` is not
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provided, ``ArrayAgg`` returned an empty list instead of ``None``. If
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you need it, explicitly set ``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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``BitXor``
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----------
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.. class:: BitXor(expression, filter=None, default=None, **extra)
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Returns an ``int`` of the bitwise ``XOR`` of all non-null input values, or
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``default`` if all values are null. It requires PostgreSQL 14+.
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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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.. code-block:: pycon
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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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.. code-block:: pycon
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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. You can query the result using :lookup:`key and index lookups
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<jsonfield.key>`.
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.. attribute:: distinct
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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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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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Usage example::
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class Room(models.Model):
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number = models.IntegerField(unique=True)
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class HotelReservation(models.Model):
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room = models.ForeignKey('Room', on_delete=models.CASCADE)
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start = models.DateTimeField()
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end = models.DateTimeField()
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requirements = models.JSONField(blank=True, null=True)
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.. code-block:: pycon
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>>> from django.contrib.postgres.aggregates import JSONBAgg
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>>> Room.objects.annotate(
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... requirements=JSONBAgg(
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... 'hotelreservation__requirements',
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... ordering='-hotelreservation__start',
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... )
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... ).filter(requirements__0__sea_view=True).values('number', 'requirements')
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<QuerySet [{'number': 102, 'requirements': [
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{'parking': False, 'sea_view': True, 'double_bed': False},
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{'parking': True, 'double_bed': True}
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]}]>
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.. versionchanged:: 5.0
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In older versions, if there are no rows and ``default`` is not
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provided, ``JSONBAgg`` returned an empty list instead of ``None``. If
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you need it, explicitly set ``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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Usage example::
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class Publication(models.Model):
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title = models.CharField(max_length=30)
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class Article(models.Model):
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headline = models.CharField(max_length=100)
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publications = models.ManyToManyField(Publication)
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.. code-block:: pycon
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>>> article = Article.objects.create(headline="NASA uses Python")
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>>> article.publications.create(title="The Python Journal")
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<Publication: Publication object (1)>
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>>> article.publications.create(title="Science News")
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<Publication: Publication object (2)>
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>>> from django.contrib.postgres.aggregates import StringAgg
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>>> Article.objects.annotate(
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... publication_names=StringAgg(
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... "publications__title",
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... delimiter=", ",
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... ordering="publications__title",
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... )
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... ).values("headline", "publication_names")
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<QuerySet [{
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'headline': 'NASA uses Python', 'publication_names': 'Science News, The Python Journal'
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}]>
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.. versionchanged:: 5.0
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In older versions, if there are no rows and ``default`` is not
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provided, ``StringAgg`` returned an empty string instead of ``None``.
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If you need it, 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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.. attribute:: sample
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Optional. By default ``CovarPop`` returns the general population
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covariance. However, if ``sample=True``, the return value will be the
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sample 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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.. code-block:: text
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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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.. code-block:: pycon
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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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.. code-block:: pycon
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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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