(Python--numpy) how to resize and slice an numpy array with out a loop?

Question

So say I have this 2d numpy array:

(
    [
        [1,2,3,4],
        [5,6,7,8],
        [9,8,7,6],
        [5,4,3,2]
    ]
);

I'd like to sub-sample this and get 2 by 2 like this (indexing every other row and every other column):

(
    [
        [1,3],
        [9,7]
    ]
)

Is there a way to do this without any loops?

Thank you!

Answer 1

Yes you can use indexing with steps (in your example step would be 2):

import numpy as np

a = np.array([[1,2,3,4], [5,6,7,8], [9,8,7,6], [5,4,3,2]])
a[::2, ::2]

returns

array([[1, 3],
       [9, 7]])

The syntax here is [dim1_start:dim1_stop:dim1_step, dim2_start:dim2_stop:dim2_step]