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Module « numpy »

Fonction bincount - module numpy

Signature de la fonction bincount

Description

help(numpy.bincount)

bincount(x, /, weights=None, minlength=0)

Count number of occurrences of each value in array of non-negative ints.

The number of bins (of size 1) is one larger than the largest value in
`x`. If `minlength` is specified, there will be at least this number
of bins in the output array (though it will be longer if necessary,
depending on the contents of `x`).
Each bin gives the number of occurrences of its index value in `x`.
If `weights` is specified the input array is weighted by it, i.e. if a
value ``n`` is found at position ``i``, ``out[n] += weight[i]`` instead
of ``out[n] += 1``.

Parameters
----------
x : array_like, 1 dimension, nonnegative ints
    Input array.
weights : array_like, optional
    Weights, array of the same shape as `x`.
minlength : int, optional
    A minimum number of bins for the output array.

Returns
-------
out : ndarray of ints
    The result of binning the input array.
    The length of `out` is equal to ``np.amax(x)+1``.

Raises
------
ValueError
    If the input is not 1-dimensional, or contains elements with negative
    values, or if `minlength` is negative.
TypeError
    If the type of the input is float or complex.

See Also
--------
histogram, digitize, unique

Examples
--------
>>> import numpy as np
>>> np.bincount(np.arange(5))
array([1, 1, 1, 1, 1])
>>> np.bincount(np.array([0, 1, 1, 3, 2, 1, 7]))
array([1, 3, 1, 1, 0, 0, 0, 1])

>>> x = np.array([0, 1, 1, 3, 2, 1, 7, 23])
>>> np.bincount(x).size == np.amax(x)+1
True

The input array needs to be of integer dtype, otherwise a
TypeError is raised:

>>> np.bincount(np.arange(5, dtype=float))
Traceback (most recent call last):
  ...
TypeError: Cannot cast array data from dtype('float64') to dtype('int64')
according to the rule 'safe'

A possible use of ``bincount`` is to perform sums over
variable-size chunks of an array, using the ``weights`` keyword.

>>> w = np.array([0.3, 0.5, 0.2, 0.7, 1., -0.6]) # weights
>>> x = np.array([0, 1, 1, 2, 2, 2])
>>> np.bincount(x,  weights=w)
array([ 0.3,  0.7,  1.1])

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