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

You can use a list comprehension to slice the array into blocks and then use the numpy.ndarray.flatten method to flatten the blocks into a 1D array (this will only work if a.shape[1] is divisible by the block size n):

import numpy as np

a = np.arange(12).reshape(3, 4)

n = 2

res = np.array([a[:, i : i + n] for i in range(0, a.shape[1], n)]).flatten()

print(res)

Output:

[ 0  1  4  5  8  9  2  3  6  7 10 11 ]