>>> x = np.eye(3)
>>> y = np.eye(3)
>>> np.where([0, 1, 0], x, y)
array([[ 1.,  0.,  0.],
       [ 0.,  1.,  0.],
       [ 0.,  0.,  1.]])
>>> np.ma.where([0, 1, 0], x, y)
Traceback (most recent call last):
  File "<pyshell#24>", line 1, in <module>
    np.ma.where([0, 1, 0], x, y)
  File "C:\Program Files\Python 3.5\lib\site-packages\numpy\ma\core.py", line 6964, in where
    np.copyto(d._data, xv.astype(ndtype), where=fc)
ValueError: could not broadcast input array from shape (3,3) into shape (3)