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I have numpy array a of shape m,n,3 and mask of shape m,n. When I try setting a[mask > 0] = (255, 0, 0) I get error 

ValueError: NumPy boolean array indexing assignment cannot assign 3 input values to the 7401 output values where the mask is true`

How can I achieve this functionality in numpy?

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  • Try numpy.ma Commented Aug 22, 2019 at 9:06
  • 1
    I cannot reproduce the issue you are seeing. Commented Aug 22, 2019 at 9:07
  • sorry, my mistake. I was indexing with mask that was m,n,3 shaped Commented Aug 22, 2019 at 10:27

1 Answer 1

Reset to default
1 
a = np.random.randint(0,2,size=(100,200,3))
mask = np.random.randint(0,2,size=(100,200))
a[mask > 0] = [255,0,0]
# Test
assert np.equal(a[mask > 0], 
    np.ones_like(a[mask > 0])*[255,0,0]).sum() == np.multiply(*a[mask > 0].shape)
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