Extract blocks or patches from NumPy Array

Question

I have a 2-d numpy array as follows:

a = np.array([[1,5,9,13],
              [2,6,10,14],
              [3,7,11,15],
              [4,8,12,16]]

I want to extract it into patches of 2 by 2 sizes with out repeating the elements.

The answer should exactly be the same. This can be 3-d array or list with the same order of elements as below:

[[[1,5],
 [2,6]],   

 [[3,7],
 [4,8]],

 [[9,13],
 [10,14]],

 [[11,15],
 [12,16]]]

How can do it easily?

In my real problem the size of a is (36, 72). I can not do it one by one. I want programmatic way of doing it.

Answer 1

Using scikit-image:

import numpy as np
from skimage.util import view_as_blocks

a = np.array([[1,5,9,13],
              [2,6,10,14],
              [3,7,11,15],
              [4,8,12,16]])

print(view_as_blocks(a, (2, 2)))