Avoiding for loop in multidimensional array

Question

So I have a 3D-array:

>>> img_data.shape
(182, 218, 182)

My idea is to replace every value equals to 0 with 255. I tried:

new_img = np.zeros(img_range)
print(new_img.shape)
for i in range(img_range[0]):
    for j in range(img_range[1]):
        for k in range(img_range[2]):
            print "%s %s %s" % (i, j, k )
            if img_data[i][j][k] == 0:
                new_img[i][j][k] = 2
            else:
                new_img[i][j][k] = img_data[i][j][k]

But this take forever, most likely because Python is dynamic and may be doing something in the backgrouns.

Any ideas on how to improve this? Thanks, Rodrigo

abc · Accepted Answer · 2018-08-31 23:43:31Z

1

You don't need to write your own loop. You can access all the elements respecting one or more conditions using the square brackets []. Check the boolean array indexing.

Example:

import numpy as np

a = np.random.randint(0, 5, size=(10, 10, 10))
a[a == 0] = -100

edited Aug 31, 2018 at 23:43

answered Aug 31, 2018 at 23:37

abc

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