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Module « numpy.matlib »

Fonction average - module numpy.matlib

Signature de la fonction average

def average(a, axis=None, weights=None, returned=False, *, keepdims=<no value>) 

Description

help(numpy.matlib.average)

Compute the weighted average along the specified axis.

Parameters
----------
a : array_like
    Array containing data to be averaged. If `a` is not an array, a
    conversion is attempted.
axis : None or int or tuple of ints, optional
    Axis or axes along which to average `a`.  The default,
    `axis=None`, will average over all of the elements of the input array.
    If axis is negative it counts from the last to the first axis.
    If axis is a tuple of ints, averaging is performed on all of the axes
    specified in the tuple instead of a single axis or all the axes as
    before.
weights : array_like, optional
    An array of weights associated with the values in `a`. Each value in
    `a` contributes to the average according to its associated weight.
    The array of weights must be the same shape as `a` if no axis is
    specified, otherwise the weights must have dimensions and shape
    consistent with `a` along the specified axis.
    If `weights=None`, then all data in `a` are assumed to have a
    weight equal to one.
    The calculation is::

        avg = sum(a * weights) / sum(weights)

    where the sum is over all included elements.
    The only constraint on the values of `weights` is that `sum(weights)`
    must not be 0.
returned : bool, optional
    Default is `False`. If `True`, the tuple (`average`, `sum_of_weights`)
    is returned, otherwise only the average is returned.
    If `weights=None`, `sum_of_weights` is equivalent to the number of
    elements over which the average is taken.
keepdims : bool, optional
    If this is set to True, the axes which are reduced are left
    in the result as dimensions with size one. With this option,
    the result will broadcast correctly against the original `a`.
    *Note:* `keepdims` will not work with instances of `numpy.matrix`
    or other classes whose methods do not support `keepdims`.

    .. versionadded:: 1.23.0

Returns
-------
retval, [sum_of_weights] : array_type or double
    Return the average along the specified axis. When `returned` is `True`,
    return a tuple with the average as the first element and the sum
    of the weights as the second element. `sum_of_weights` is of the
    same type as `retval`. The result dtype follows a general pattern.
    If `weights` is None, the result dtype will be that of `a` , or ``float64``
    if `a` is integral. Otherwise, if `weights` is not None and `a` is non-
    integral, the result type will be the type of lowest precision capable of
    representing values of both `a` and `weights`. If `a` happens to be
    integral, the previous rules still applies but the result dtype will
    at least be ``float64``.

Raises
------
ZeroDivisionError
    When all weights along axis are zero. See `numpy.ma.average` for a
    version robust to this type of error.
TypeError
    When `weights` does not have the same shape as `a`, and `axis=None`.
ValueError
    When `weights` does not have dimensions and shape consistent with `a`
    along specified `axis`.

See Also
--------
mean

ma.average : average for masked arrays -- useful if your data contains
             "missing" values
numpy.result_type : Returns the type that results from applying the
                    numpy type promotion rules to the arguments.

Examples
--------
>>> import numpy as np
>>> data = np.arange(1, 5)
>>> data
array([1, 2, 3, 4])
>>> np.average(data)
2.5
>>> np.average(np.arange(1, 11), weights=np.arange(10, 0, -1))
4.0

>>> data = np.arange(6).reshape((3, 2))
>>> data
array([[0, 1],
       [2, 3],
       [4, 5]])
>>> np.average(data, axis=1, weights=[1./4, 3./4])
array([0.75, 2.75, 4.75])
>>> np.average(data, weights=[1./4, 3./4])
Traceback (most recent call last):
    ...
TypeError: Axis must be specified when shapes of a and weights differ.

With ``keepdims=True``, the following result has shape (3, 1).

>>> np.average(data, axis=1, keepdims=True)
array([[0.5],
       [2.5],
       [4.5]])

>>> data = np.arange(8).reshape((2, 2, 2))
>>> data
array([[[0, 1],
        [2, 3]],
       [[4, 5],
        [6, 7]]])
>>> np.average(data, axis=(0, 1), weights=[[1./4, 3./4], [1., 1./2]])
array([3.4, 4.4])
>>> np.average(data, axis=0, weights=[[1./4, 3./4], [1., 1./2]])
Traceback (most recent call last):
    ...
ValueError: Shape of weights must be consistent
with shape of a along specified axis.

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