Delete element from multi-dimensional numpy array by value

Question

Given a numpy array

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

what\'s the fastest way to delete all elements of value -1

Answer 1

For almost everything you might want to do with such an array, you can use a masked array

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

b=np.ma.masked_equal(a,-1)

b
Out[5]: 
masked_array(data =
 [[0 -- 0]
 [1 0 0]
 [1 0 --]],
             mask =
 [[False  True False]
 [False False False]
 [False False  True]],
       fill_value = -1)

If you really want the ragged array, it can be .compressed() by line

c=np.array([b[i].compressed() for i in range(b.shape[0])])

c
Out[10]: array([array([0, 0]), array([1, 0, 0]), array([1, 0])], dtype=object)