How to find maximum negative and minimum positive number in a numpy array?

Question

I am given an array containing both positive and negative numbers.

import numpy as np
arr = np.array([-10.2, -5.3, -2.1, 0, 1.2, 3.4])

I would like to find the index corresponding to the maximum negative number and to a minimum positive number. In the above, my expected outcome is 2 and 4. Is there any numpy trick to achieve this? I have found a solution in this link, but I would like to know how this could be done through numpy functions: Finding index of largest negative and smallest positive element in array

Answer 1

Replace non negative values with -inf, then use argmax to find the largest negative:

np.where(arr < 0, arr, -np.inf).argmax()
# 2

Similarly replace non positive values with inf then use argmin to find the smallest positive:

np.where(arr > 0, arr, np.inf).argmin()
# 4