numpy mask indexing code example

Example: how to get single element from arraylist in numpy arrayt

>>> import numpy as np
>>> np_arr = np.array([[1,2,3], [4,5,6], [7,8,9]])
>>> np_arr
array([[1, 2, 3],
       [4, 5, 6],
       [7, 8, 9]])
>>> arr = [ele[0] for ele in np_arr]
>>> arr
[1, 4, 7]