numpy reverse multidimensional array

Question

What is the simplest way in numpy to reverse the most inner values of an array like this:

array([[[1, 1, 1, 2],     [2, 2, 2, 3],     [3, 3, 3, 4]],     [[1, 1, 1, 2],     [2, 2, 2, 3],     [3, 3, 3, 4]]]) 

so that I get the following result:

array([[[2, 1, 1, 1],     [3, 2, 2, 2],     [4, 3, 3, 3]],     [[2, 1, 1, 1],     [3, 2, 2, 2],     [4, 3, 3, 3]]]) 

Thank you very much!

Answer 1

How about:

import numpy as np a = np.array([[[10, 1, 1, 2],                [2, 2, 2, 3],                [3, 3, 3, 4]],               [[1, 1, 1, 2],                [2, 2, 2, 3],                [3, 3, 3, 4]]]) 

and the reverse along the last dimension is:

b = a[:,:,::-1] 

or

b = a[...,::-1] 

although I like the later less since the first two dimensions are implicit and it is more difficult to see what is going on.

Answer 2

For each of the inner array you can use fliplr. It flips the entries in each row in the left/right direction. Columns are preserved, but appear in a different order than before.

Sample usage:

import numpy as np initial_array = np.array([[[1, 1, 1, 2],                           [2, 2, 2, 3],                           [3, 3, 3, 4]],                          [[1, 1, 1, 2],                           [2, 2, 2, 3],                           [3, 3, 3, 4]]]) index=0 initial_shape = initial_array.shape reversed=np.empty(shape=initial_shape) for inner_array in initial_array:     reversed[index] = np.fliplr(inner_array)     index += 1 

printing reversed

Output:

array([[[2, 1, 1, 1],         [3, 2, 2, 2],         [4, 3, 3, 3]],        [[2, 1, 1, 1],         [3, 2, 2, 2],         [4, 3, 3, 3]]]) 

Make sure your input array for fliplr function must be at least 2-D.

Moreover if you want to flip array in the up/down direction. You can also use flipud