numpy.random.choice和zeros的用法

numpy.random.choice

numpy.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.

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 was np.arange(n) 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 : 1-D ndarray, shape (size,) 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

Ex
4000
amples
Generate a uniform random sample from np.arange(5) of size 3:

>>>

>>> np.random.choice(5, 3)
array([0, 3, 4])
>>> #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])

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])
>>> #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])

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'],
dtype='|S11')

用法：zeros(shape, dtype=float, order='C')返回：返回来一个给定形状和类型的用0填充的数组；参数：shape:形状            dtype:数据类型，可选参数，默认numpy.float64            dtype类型：t ,位域,如t4代表4位                                 b,布尔值，true or false                                 i,整数,如i8(64位）                                u,无符号整数，u8(64位）                                f,浮点数，f8（64位）                               c,浮点负数，                                o,对象，                               s,a，字符串，s24                               u,unicode,u24            order:可选参数，c代表与c语言类似，行优先；F代表列优先