Replacing elements in an array from index array

Question

I have two 2D arrays like:

A=array[[4,5,6],
        [0,7,8],
        [0,9,0]]

B = array[[11,12,13],
          [14,15,16],
          [17,18,19]]

In array A where element value is 0 i want to replace same value in array B by 0 and store the changed matrix in a new variable and retain the old B matrix.

Thanks in advance.

Possible duplicate of [Replacing Numpy elements if condition is met](https://stackoverflow.com/questions/19766757/replacing-numpy-elements-if-condition-is-met) — Sheldore, May 26 '19 at 09:36

Akash Basudevan · Accepted Answer · 2019-05-26T11:01:53.073

5

import numpy as np
A=np.array([[4,5,6],
    [0,7,8],
    [0,9,0]])

B =np.array([[11,12,13],
      [14,15,16],
      [17,18,19]])
C = B.copy()
B[A == 0] = 0
C, B = B, C

The line B[A == 0] basically first gets all the the values where the array A is 0 by the line A == 0 . It return a boolean array with true at the position where value is zero in array A. This boolean array is then used to mask the array B and assigns 0 to indices the boolean values is True.

edited May 26 '19 at 11:01

answered May 26 '19 at 09:30

Akash Basudevan

820
5
15

Not sure why you got downvoted. This is about as concise as you can get... +1 – Mad Physicist May 26 '19 at 09:35
Well, I didn't downvote but I think one reason could be that there is no explanation whatsoever in your code regarding the last line +1 from me. May be you can add some explanation – Sheldore May 26 '19 at 09:37
But I want to retain old B matrix also. But this changes it. – Nick May 26 '19 at 10:29
I dont understand . "In array A where element value is 0 i want to replace same value in array B by 0." You want a new matrix with those values ? – Akash Basudevan May 26 '19 at 10:32
Yes exactly, I want new matrix with those values – Nick May 26 '19 at 10:59
Edited. You have your values in matrix C. It would be really great if you could mark this answer as the accepted answer. – Akash Basudevan May 26 '19 at 11:04

Replacing elements in an array from index array

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