masking elements in an array using numpy

Question

I am trying to mask some elements in an array such that a mathematical operation is not applied to these elements.

I ran this code

import numpy as np

inp = np.random.randn(5, 5)
c = np.random.randn(5,5)
mask = inp > 0


inp[mask] += c

print(inp)

but I got this error

ValueError: operands could not be broadcast together with shapes (25,) (5,5) (25,)

Have you checked the shape of input[mask] to see if it looks like you expect? — G. Anderson
– G. Anderson, Commented Apr 29, 2021 at 17:21
You can't add arrays of different shapes that are not broadcastable. — Lith
– Lith, Commented Apr 29, 2021 at 17:22
Also worth noting: Don't name variables the same as built-in functions, like input in your case would shadow the built-in input function — G. Anderson
– G. Anderson, Commented Apr 29, 2021 at 17:22

Woodford · Accepted Answer · 2021-04-29 17:30:37Z

1

inp += mask.astype(int) * c

# -- or simplified to:
inp += mask * c

answered Apr 29, 2021 at 17:30

Woodford

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