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Module « numpy.matlib »

Fonction count_nonzero - module numpy.matlib

Signature de la fonction count_nonzero

def count_nonzero(a, axis=None, *, keepdims=False) 

Description

help(numpy.matlib.count_nonzero)

Counts the number of non-zero values in the array ``a``.

The word "non-zero" is in reference to the Python 2.x
built-in method ``__nonzero__()`` (renamed ``__bool__()``
in Python 3.x) of Python objects that tests an object's
"truthfulness". For example, any number is considered
truthful if it is nonzero, whereas any string is considered
truthful if it is not the empty string. Thus, this function
(recursively) counts how many elements in ``a`` (and in
sub-arrays thereof) have their ``__nonzero__()`` or ``__bool__()``
method evaluated to ``True``.

Parameters
----------
a : array_like
    The array for which to count non-zeros.
axis : int or tuple, optional
    Axis or tuple of axes along which to count non-zeros.
    Default is None, meaning that non-zeros will be counted
    along a flattened version of ``a``.
keepdims : bool, optional
    If this is set to True, the axes that are counted are left
    in the result as dimensions with size one. With this option,
    the result will broadcast correctly against the input array.

Returns
-------
count : int or array of int
    Number of non-zero values in the array along a given axis.
    Otherwise, the total number of non-zero values in the array
    is returned.

See Also
--------
nonzero : Return the coordinates of all the non-zero values.

Examples
--------
>>> import numpy as np
>>> np.count_nonzero(np.eye(4))
4
>>> a = np.array([[0, 1, 7, 0],
...               [3, 0, 2, 19]])
>>> np.count_nonzero(a)
5
>>> np.count_nonzero(a, axis=0)
array([1, 1, 2, 1])
>>> np.count_nonzero(a, axis=1)
array([2, 3])
>>> np.count_nonzero(a, axis=1, keepdims=True)
array([[2],
       [3]])

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