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 so

Answer 1

Here's a naive one-liner:

[any (value in item for value in v) for item in A]

Sample output:

>>> A = ( [0,1,2], [1,2,3], [2,3,4] )
>>> v = [1,2]
>>> [any (value in item for value in v) for item in A]
[True, True, True]
>>> v = [1]
>>> [any (value in item for value in v) for item in A]
[True, True, False]

It's a very Pythonic approach, but I'm certain it won't scale well on large arrays or vectors because Python's in operator is a linear search (on lists/tuples, at least).

As Brooks Moses pointed out in the below comment, the output should be a 3x3 matrix. That's why you give sample output in your questions. (Thanks Brooks)

>>> v=[1,2]
>>> [ [item in v for item in row] for row in A]
[[False, True, True], [True, True, False], [True, False, False]]
>>> v=[1]
>>> [ [item in v for item in row] for row in A]
[[False, True, False], [True, False, False], [False, False, False]]