Question

Still trying to earn my numpy stripes: I want to perform an arithmetic operation on two numpy arrays, which is simple enough:

return 0.5 * np.sum(((array1 - array2) ** 2) / (array1 + array2))

Problem is, I need to be able to specify the condition that, if both arrays are element-wise 0 at the same element i, don’t perform the operation at all–would be great just to return 0 on this one–so as not to divide by 0.

However, I have no idea how to specify this condition without resorting to the dreaded nested for-loop. Thank you in advance for your assistance.

Edit: Would also be ideal not to have to resort to a pseudocount of +1.

Answer 1

Just replace np.sum() by np.nansum():

return 0.5 * np.nansum(((array1 - array2) ** 2) / (array1 + array2))

np.nansum() treats nans as zero.