将 3D 矩阵转换为垂直级联的 1D 阵列

Question

Is there any shortcut to the for loop in the following piece of code?

import numpy as np

ff = np.zeros((3,3,4))
gg = np.zeros((36,1))

ff[:,:,0] = 1
ff[:,:,1] = 2
ff[:,:,2] = 3
ff[:,:,3] = 4


for ii in xrange(4):
    gg[ii*9:(ii+1)*9,0] = ff[:,:,ii].reshape((9,))

Answer 1

You can use transpose or swapaxes with some reshaping -

ff.transpose([2,1,0]).ravel()[:,None]

ff.swapaxes(0,2).ravel()[:,None]

You can replace the ravel with reshape -

ff.transpose([2,1,0]).reshape(-1,1)

ff.swapaxes(0,2).reshape(-1,1)