python create subset of array from boolean column mask

Question

I need to create a function or equation that will turn this input...

a = [True, False, True]
b = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

into this output...

c = [[1, 3], [4, 6], [7, 9]]

Note: the above arrays are all numpy arrays. Thanks!

Something like [[e for x, e in zip(a, sublist) if x] for sublist in b] will work but I suspect there's a more efficent numpy solution — Patrick Haugh
– Patrick Haugh, Commented Oct 2, 2017 at 18:25

BENY · Accepted Answer · 2017-10-02 18:28:19Z

7

numpy solution

import numpy as np 
a = np.array([True, False, True])
b = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
b[:,a]

array([[1, 3],
       [4, 6],
       [7, 9]])

answered Oct 2, 2017 at 18:28

BENY

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1 Comment

Vaishali Over a year ago

Nice, makes much more sense +1

Vaishali · Accepted Answer · 2017-10-02 18:25:10Z

2

You can use itertools compress

from itertools import compress
c = [list(compress(i, a)) for i in b]

[[1, 3], [4, 6], [7, 9]]

answered Oct 2, 2017 at 18:25

Vaishali

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