reshaping 2D numpy array

[perfringo]

You can grab indices and using vstack and ravel get desired result:

import numpy as np

arr = np.array([[0, 0, -1],   
              [0, 0, -1], 
              [0, 0, 0], 
              [0, 0, 0],    
              [0, 0, 1],
              [0, 0, 1]])

arr_2 = np.vstack((arr[::2].ravel(), arr[1::2].ravel()))

# arr_2
[[ 0  0 -1  0  0  0  0  0  1]
 [ 0  0 -1  0  0  0  0  0  1]]

But this feels too brute-force. Therefore alternative could be preferred:

arr_3 = arr.reshape(-1, 2, 3).swapaxes(0, 1).reshape(2, -1)