numpy.random.choice#
- random.choice(a, size=None, replace=True, p=None)#
Generates a random sample from a given 1-D array
New in version 1.7.0.
Note
New code should use the
choice
method of aGenerator
instance instead; please see the Quick Start.- Parameters:
- a1-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 it were
np.arange(a)
- sizeint or tuple of ints, optional
Output shape. If the given shape is, e.g.,
(m, n, k)
, thenm * n * k
samples are drawn. Default is None, in which case a single value is returned.- replaceboolean, optional
Whether the sample is with or without replacement. Default is True, meaning that a value of
a
can be selected multiple times.- p1-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:
- samplessingle 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
random.Generator.choice
which should be used in new code
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 ofp
is 1 / len(a).Sampling random rows from a 2-D array is not possible with this function, but is possible with
Generator.choice
through itsaxis
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')