Remove alternate columns and row of 2d numpy array

Question

I have a problem where I need to remove alternate columns and rows of a 2D numpy array.

I've tried using numpy.delete to do so but the results didn't turn out what I want to be...

for x in range(rows):
    if x %2 ==0:
        array_np=np.delete(array_np,1,axis=1)
for y in range(columns):
    if y %2 ==0:
        array_np=np.delete(array_np,1,axis=0)

for eg.

[[1,2,3,4],

 [5,6,7,8],

 [9,10,11,12],

 [13,14,15,16]]

expected output:

[[1,3],

 [9,11]]

The array is quite large in size than this, but the idea is the same.

You should look at: stackoverflow.com/questions/16632568/… might be helpful — mucka
– mucka, Commented Feb 6, 2019 at 8:03
I did, but that's kinda static. I have a large array and need to delete every alternate row and column from it. — sspatole
– sspatole, Commented Feb 6, 2019 at 8:04

overfit · Accepted Answer · 2019-02-06 08:23:10Z

2

import numpy as np

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

arr_all_odd=np.delete(arr_np, list(range(1, arr_np.shape[0], 2)), axis=1)
arr_odd_odd=np.delete(arr_all_odd, list(range(1, arr_np.shape[1], 2)), axis=0)

print(arr_odd_odd)

Output:

[[ 1  3]
 [ 9 11]]

You can make arr_odd_even, arr_even_odd, or arr_even_even in the same way.

answered Feb 6, 2019 at 8:23

overfit

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Comments

mucka · Accepted Answer · 2019-02-06 08:22:54Z

1

You can try generating odd number list using list(range(1, array.shape[0], 2)), then you can construct list of all columns you need to delete.

a = np.array([[1,2,3,4],
...  [5,6,7,8],
...  [9,10,11,12],
...  [13,14,15,16]])
>>> np.delete(a, range(1, a.shape[0], 2), axis=0)
array([[ 1,  2,  3,  4],
       [ 9, 10, 11, 12]])
>>> np.delete(a, range(1, a.shape[1], 2), axis=1)
array([[ 1,  3],
       [ 5,  7],
       [ 9, 11],
       [13, 15]])

If you combine both you should achieve what I understand you want.

answered Feb 6, 2019 at 8:22

mucka

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