user3176697 user3176697 - 2 months ago 27
Python Question

Delete rows from numpy array depending on a condition on a single cell

Above all, sorry for my bad English.

I have this array

t
:

array([[ 0, 1, 2, 0, 4, 5, 6, 7, 8, 9],
[ 0, 11, 0, 13, 0, 15, 0, 17, 18, 0]])


I would like to delete the columns where the value of second line is null. Here, I would like to delete the columns 0, 2, 4, 6 and 9, to obtain this array:

array([[ 1, 0, 5, 7, 8 ],
[ 11, 13, 15, 17, 18 ]])


I tried with
np.sum()
but didn't succeed.

Answer

Similar to Juh_, but more expressive, and avoiding some minor unnecessary performance overhead. A grand total of 12 highly pythonic, explicit and unambigious characters. This is really numpy 101; if you are still trying to wrap your head around this, you would do yourself a favor by reading a numpy primer.

import numpy as np
a = np.array([[ 0,  1,  2,  0,  4,  5,  6,  7,  8,  9],
              [ 0, 11,  0, 13,  0, 15,  0, 17, 18,  0]])
print a[:,a[1]!=0]
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