[FIXED] Change 1's to 0 and 0's to 1 in numpy array without looping

Issue

Lets say i have a numpy Array where i would like to swap all the 1's to 0 and all the 0's to a 1 (the array will have other values, and there is nothing special about the 0's and 1's). Ofcourse i can loop through the array and change it 1 by 1. Is there an efficient method you can recommend using? does the np.where() method have an option for this operation?

Solution

A very simple way which does not require the use of any special method such as np.where() is to get the indices for the conditions of the variables in your numpy array, and accordingly assign the required value (in your case 0 for 1s and 1 for 0s) to the respective positional items in the array. This works for values other than 0s and 1s too. Also, you don't require any temporary variable to swap the values.

import numpy as np
arr = np.array([1, 0, 2, 3, 6, 1, 0])
indices_one = arr == 1
indices_zero = arr == 0
arr[indices_one] = 0 # replacing 1s with 0s
arr[indices_zero] = 1 # replacing 0s with 1s

Output: array([0, 1, 2, 3, 6, 0, 1])

Answered By - JChat