Rotate 2D axis around the central x axis

Question

I have a simple 2D array:

array([[ 1,  2,  3,  4],
       [ 5,  6,  7,  8],
       [ 9, 10, 11, 12]])

And would like it to be:

array([[ 9,  10,  11,  12],
       [ 5,  6,  7,  8],
       [ 1, 2, 3, 4]])

How could this be done, and then, in general, how could this be done for an [n,m] sort of array?

Answer 1

You can use np.flipud (up/down) or with similar result np.flip on the axis=0:

import numpy as np

arr = np.array([[ 1,  2,  3,  4],
                [ 5,  6,  7,  8],
                [ 9, 10, 11, 12]])

flipud_arr = np.flipud(arr)
print(flipud_arr)    

flip_arr = np.flip(arr, axis=0)
print(flip_arr)

Both have the same output:

array([[ 9, 10, 11, 12],
       [ 5,  6,  7,  8],
       [ 1,  2,  3,  4]])

---

Both work in general, so also for even rows:

arr = np.array([[ 1,  2,  3,  4],
                [ 5,  6,  7,  8],
                [ 9, 10, 11, 12],
                [ 3,  0,  8,  1]])
np.flipud(arr)  # in place = same memory, for copy see 1st code snippet

Output:

array([[ 3,  0,  8,  1],
       [ 9, 10, 11, 12],
       [ 5,  6,  7,  8],
       [ 1,  2,  3,  4]])