arrays - How can I implement matlabs ``ismember()`` command in Python?

Question

here is my problem: I would like to create a boolean matrix B that contains True everywhere that matrix A has a value contained in vector v. One inconvenient solution would be:

import numpy as np
>>> A = np.array([[0,1,2], [1,2,3], [2,3,4]])
array([[0, 1, 2],
       [1, 2, 3],
       [2, 3, 4]])
>>> v = [1,2]
>>> B = (A==v[0]) + (A==v[1]) # matlab: ``B = ismember(A,v)``
array([[False,  True,  True],
       [ True,  True, False],
       [ True, False, False]], dtype=bool)

Is there maybe a solution that would be more convenient if A and v would have more values?

Cheers!

Answer 1

I don't know much numpy, be here's a raw python one:

>>> A = [[0,1,2], [1,2,3], [2,3,4]]
>>> v = [1,2]
>>> B = [map(lambda val: val in v, a) for a in A]
>>>
>>> B
[[False, True, True], [True, True, False], [True, False, False]]

Edit: As Brooks Moses notes and some simple timing seems to show, this one is probably be better:

>>> B = [ [val in v for val in a] for a in A]