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Classe « Generator »

Méthode numpy.random.Generator.choice

Signature de la méthode choice

def choice(self, a, size=None, replace=True, p=None, axis=0, shuffle=True) 

Description

help(Generator.choice)

        choice(a, size=None, replace=True, p=None, axis=0, shuffle=True)

        Generates a random sample from a given array

        Parameters
        ----------
        a : {array_like, int}
            If an ndarray, a random sample is generated from its elements.
            If an int, the random sample is generated from np.arange(a).
        size : {int, tuple[int]}, optional
            Output shape.  If the given shape is, e.g., ``(m, n, k)``, then
            ``m * n * k`` samples are drawn from the 1-d `a`. If `a` has more
            than one dimension, the `size` shape will be inserted into the
            `axis` dimension, so the output ``ndim`` will be ``a.ndim - 1 +
            len(size)``. Default is None, in which case a single value is
            returned.
        replace : bool, optional
            Whether the sample is with or without replacement. Default is True,
            meaning that a value of ``a`` can be selected multiple times.
        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``.
        axis : int, optional
            The axis along which the selection is performed. The default, 0,
            selects by row.
        shuffle : bool, optional
            Whether the sample is shuffled when sampling without replacement.
            Default is True, False provides a speedup.

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

        Raises
        ------
        ValueError
            If a is an int and less than zero, if p is not 1-dimensional, if
            a is array-like with a 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
        --------
        integers, shuffle, permutation

        Notes
        -----
        Setting user-specified probabilities through ``p`` uses a more general but less
        efficient sampler than the default. The general sampler produces a different sample
        than the optimized sampler even if each element of ``p`` is 1 / len(a).

        ``p`` must sum to 1 when cast to ``float64``. To ensure this, you may wish
        to normalize using ``p = p / np.sum(p, dtype=float)``.

        When passing ``a`` as an integer type and ``size`` is not specified, the return
        type is a native Python ``int``.

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

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

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

        >>> rng.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:

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

        Generate a uniform random sample from a 2-D array along the first
        axis (the default), without replacement:

        >>> rng.choice([[0, 1, 2], [3, 4, 5], [6, 7, 8]], 2, replace=False)
        array([[3, 4, 5], # random
               [0, 1, 2]])

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

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

        

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