Module « numpy.random »

Fonction choice - module numpy.random

Signature de la fonction choice

Description

choice.__doc__

        choice(a, size=None, replace=True, p=None)

        Generates a random sample from a given 1-D array

        .. versionadded:: 1.7.0

        .. note::
            New code should use the ``choice`` method of a ``default_rng()``
            instance instead; please see the :ref:`random-quick-start`.

        Parameters
        ----------
        a : 1-D array-like or int
            If an ndarray, a random sample is generated from its elements.
            If an int, the random sample is generated as if a were np.arange(a)
        size : int or tuple of ints, optional
            Output shape.  If the given shape is, e.g., ``(m, n, k)``, then
            ``m * n * k`` samples are drawn.  Default is None, in which case a
            single value is returned.
        replace : boolean, optional
            Whether the sample is with or without replacement
        p : 1-D array-like, optional
            The probabilities associated with each entry in a.
            If not given the sample assumes a uniform distribution over all
            entries in a.

        Returns
        -------
        samples : single item or ndarray
            The generated random samples

        Raises
        ------
        ValueError
            If a is an int and less than zero, if a or p are not 1-dimensional,
            if a is an array-like of size 0, if p is not a vector of
            probabilities, if a and p have different lengths, or if
            replace=False and the sample size is greater than the population
            size

        See Also
        --------
        randint, shuffle, permutation
        Generator.choice: which should be used in new code

        Notes
        -----
        Sampling random rows from a 2-D array is not possible with this function,
        but is possible with `Generator.choice` through its ``axis`` keyword.

        Examples
        --------
        Generate a uniform random sample from np.arange(5) of size 3:

        >>> np.random.choice(5, 3)
        array([0, 3, 4]) # random
        >>> #This is equivalent to np.random.randint(0,5,3)

        Generate a non-uniform random sample from np.arange(5) of size 3:

        >>> np.random.choice(5, 3, p=[0.1, 0, 0.3, 0.6, 0])
        array([3, 3, 0]) # random

        Generate a uniform random sample from np.arange(5) of size 3 without
        replacement:

        >>> np.random.choice(5, 3, replace=False)
        array([3,1,0]) # random
        >>> #This is equivalent to np.random.permutation(np.arange(5))[:3]

        Generate a non-uniform random sample from np.arange(5) of size
        3 without replacement:

        >>> np.random.choice(5, 3, replace=False, p=[0.1, 0, 0.3, 0.6, 0])
        array([2, 3, 0]) # random

        Any of the above can be repeated with an arbitrary array-like
        instead of just integers. For instance:

        >>> aa_milne_arr = ['pooh', 'rabbit', 'piglet', 'Christopher']
        >>> np.random.choice(aa_milne_arr, 5, p=[0.5, 0.1, 0.1, 0.3])
        array(['pooh', 'pooh', 'pooh', 'Christopher', 'piglet'], # random
              dtype='<U11')