Indexing numpy array using boolean vector

Question

I have a numpy.ndarray and I have a boolean list. I want to use the list to access the columns in the array.

X = [[1,2,3,4],[5,6,7,8]]
Y = [True,False,False,True]

I want the result to be

[[1,4][5,8]]

I guess I am doing this inefficiently and would like to know if there is a straightforward method.

@Nivi, Divakar's answer should work, unless your sample input does not reflect your actual data's characteristics. I'd advise you to revisit your question. — cs95
– cs95, Commented Oct 26, 2017 at 16:50

utengr · Accepted Answer · 2017-10-26 16:46:28Z

2

You have to convert it to numpy first.

import numpy as np

X = np.array([[1,2,3,4],[5,6,7,8]])
Y = np.array([True,False,False,True])

print(X[:,Y])

answered Oct 26, 2017 at 16:46

utengr

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4 Comments

did you convert your array into numpy?

I did the copy/paste, and it works just as you'd like.

Yes it does. My y = array([ True, False, True, False], dtype=bool) Will check. Thanks.

@ it should be np.array, not just array. Can you please put your actual code in the question? if it is still not working.