Flatten or group array in blocks of columns - NumPy / Python

Question

Is there any easy way to flatten

import numpy    
np.arange(12).reshape(3,4)
Out[]: 
array([[ 0,  1,  2,  3],
       [ 4,  5,  6,  7],
       [ 8,  9, 10, 11         


        

Answer 1

For this I'd simply slice and concatenate:

n = a.shape[1]//2
np.concatenate([a[:,:n], a[:,n:]]).ravel()
# array([ 0,  1,  4,  5,  8,  9,  2,  3,  6,  7, 10, 11])