python - 访问 numpy ndarray 中的单个列

Question

我有一个形状为 (m, 1,100,4) 的 nd-numpy 数组我想访问内部数组的各个列(形状: (1,100,4) )。
MWE:
例如，假设我有这个:

import numpy as np
X = np.random.randn(2, 1, 5, 4)
    
X
array([[[[-0.40867508,  0.09331783,  1.26134307, -1.18900601],
         [-0.79177772,  0.96738931, -0.33332772,  0.53130287],
         [ 3.67290383,  0.30954936,  0.63221306, -0.64003826],
         [-1.20878773,  1.21499506,  1.84995811,  0.15663168],
         [-0.60648072, -0.30464852, -0.44044224, -4.46482868]]],


       [[[-1.90531392, -0.47108517,  1.21177166,  0.09561669],
         [ 3.21803694,  0.30611821,  1.71334417,  0.73383279],
         [-1.12869017, -0.1497266 , -0.54913676,  0.36704922],
         [ 0.5652546 , -0.75012341, -0.72496611,  1.12428097],
         [-1.19727408, -0.13813127,  2.63948821, -0.37661527]]]])

嵌套数组的形状 (1,5,4) .然后访问每个嵌套数组的第一列返回整个数组:

X[ :, 0]
array([[[-0.40867508,  0.09331783,  1.26134307, -1.18900601],
        [-0.79177772,  0.96738931, -0.33332772,  0.53130287],
        [ 3.67290383,  0.30954936,  0.63221306, -0.64003826],
        [-1.20878773,  1.21499506,  1.84995811,  0.15663168],
        [-0.60648072, -0.30464852, -0.44044224, -4.46482868]],

       [[-1.90531392, -0.47108517,  1.21177166,  0.09561669],
        [ 3.21803694,  0.30611821,  1.71334417,  0.73383279],
        [-1.12869017, -0.1497266 , -0.54913676,  0.36704922],
        [ 0.5652546 , -0.75012341, -0.72496611,  1.12428097],
        [-1.19727408, -0.13813127,  2.63948821, -0.37661527]]])

我的目的是得到一个元组，这样:

s,t,u,v = X[first_columns], X[second_columns], X[third_columns], X[fouth_columns]

使得:

s =[-0.40867508, -0.79177772, 3.67290383, -1.20878773, -0.60648072,
   -1.90531392, 3.21803694, -1.12869017, 0.5652546, -1.19727408]

Answer 1

你要找的是

X[:,0,:,0].ravel()

请注意，这种形状的 X ，我们不能直接以数组的形式获取所需的元素，而是以二维矩阵的形式获取。因此我们需要 reshape以数组形式。
另一个对应于:

t = X[:,0,:,1].ravel()
u = X[:,0,:,2].ravel()
v = X[:,0,:,3].ravel()