Change values of all elements in a numpy sub array given a condition

Question

Let's say I have a 3d numpy ndarray with the shape 5x7x3

import numpy as np

arr = np.random.rand(5,7,3)

What I would like to do is:

Take every sub-array
Find out if the first value in a sub-array is larger than the sum of the last to elements.
If the condition is true then I would like to change of all three elements in the sub-array to the same value (eg. 2).

Adhun Thalekkara · Accepted Answer · 2020-08-07 10:34:16Z

1

you can do something like this

import numpy as np

arr = np.random.randint(5,size=(5,7,3))
print(arr)
for i in range(len(arr)):
    for j in range(len(arr[i])):
        if arr[i][j][0]<arr[i][j][-1]+arr[i][j][-2]:
            arr[i][j]=[2,2,2]
print('updated array',arr)

output

[[[0 2 1]
  [0 2 3]
  [2 3 0]
  [1 0 0]
  [2 2 3]
  [1 4 2]
  [3 3 4]]

 [[3 1 0]
  [1 4 3]
  [0 1 1]
  [4 2 2]
  [1 1 0]
  [2 1 3]
  [0 4 3]]

 [[2 3 1]
  [0 4 4]
  [2 1 2]
  [4 3 2]
  [2 3 4]
  [0 2 3]
  [3 4 1]]

 [[0 4 1]
  [2 0 0]
  [2 2 3]
  [0 2 3]
  [0 4 4]
  [0 4 0]
  [1 2 3]]

 [[4 0 0]
  [3 4 1]
  [2 2 4]
  [3 0 4]
  [1 2 3]
  [4 3 1]
  [4 3 4]]]
dsfs [[[2 2 2]
  [2 2 2]
  [2 2 2]
  [1 0 0]
  [2 2 2]
  [2 2 2]
  [2 2 2]]

 [[3 1 0]
  [2 2 2]
  [2 2 2]
  [4 2 2]
  [1 1 0]
  [2 2 2]
  [2 2 2]]

 [[2 2 2]
  [2 2 2]
  [2 2 2]
  [2 2 2]
  [2 2 2]
  [2 2 2]
  [2 2 2]]

 [[2 2 2]
  [2 0 0]
  [2 2 2]
  [2 2 2]
  [2 2 2]
  [2 2 2]
  [2 2 2]]

 [[4 0 0]
  [2 2 2]
  [2 2 2]
  [2 2 2]
  [2 2 2]
  [4 3 1]
  [2 2 2]]]

answered Aug 7, 2020 at 10:34

Adhun Thalekkara

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2 Comments

user498823 Over a year ago

I can see that it would work, but i was hoping that there was a faster build-in funktion.

Adhun Thalekkara Over a year ago

I believe ur case is custom requirememt

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