Update array based on other array Python

Question

I have two arrays of the same size:

import numpy as np
myArray = np.array([[5,3,2,1,2],
                    [2,5,3,3,3]])

myotherArray = np.array([[0,1,1,0,0],
                         [0,0,1,0,0]])

I like to multiple all values in myArray by 5, but only if on the same index in myotherArray a value of 0 is. How do I do this? I tried this, but it doesn't do anything.

myArray[myotherArray == 0]*5

My expected output is for myArray

([[25,3,2,5,10],
  [10,25,3,15,15]])

Daniel · Accepted Answer · 2013-11-28 00:24:18Z

4

Multiply in place:

>>> myArray[myotherArray == 0] *= 5
>>> myArray
array([[25,  3,  2,  5, 10],
       [10, 25,  3, 15, 15]])

answered Nov 28, 2013 at 0:24

Daniel

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mgilson · Accepted Answer · 2013-11-28 00:24:19Z

3

Not sure if this is the most efficient way to do it, but:

>>> myArray * np.where(myotherArray == 0, 5, 1)
array([[25,  3,  2,  5, 10],
       [10, 25,  3, 15, 15]])

Another alternative:

>>> np.where(myotherArray == 0, 5*myArray, myArray)
array([[25,  3,  2,  5, 10],
       [10, 25,  3, 15, 15]])

answered Nov 28, 2013 at 0:24

mgilson

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