Replace elements of particular axis index in n-dimensional numpy array

Question

Given an n-dimensional numpy array. Now an axis and corresponding index is given. All elements in that particular axis-index should be replaced by given value. Example of an three-dimensional array:

>>a = np.ones((2,2,2))
array([[[ 1.,  1.],
        [ 1.,  1.]],

        [[ 1.,  1.],
        [ 1.,  1.]]])

Given axis=1, index=0. All elements in this axis-index needs to be zero.

>>a
array([[[ 0.,  0.],
        [ 1.,  1.]],

       [[ 0.,  0.],
        [ 1.,  1.]]])

Paul Panzer · Accepted Answer · 2018-05-30 15:41:49Z

5

Use swapaxes:

a.swapaxes(0, axis)[index] = value

Example:

>>> import numpy as np
>>> a = np.zeros((2,3,4))
>>> a.swapaxes(0, 1)[2] = 3
>>> a
array([[[0., 0., 0., 0.],
        [0., 0., 0., 0.],
        [3., 3., 3., 3.]],

       [[0., 0., 0., 0.],
        [0., 0., 0., 0.],
        [3., 3., 3., 3.]]])

edited May 30, 2018 at 15:41

answered May 30, 2018 at 15:34

Paul Panzer

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Comments

Ben.T · Accepted Answer · 2018-05-30 15:14:02Z

0

you can do a[:,0,:] = 0 and you get your output, where in a[:,0,:] you select index = 0 of the axis=1 and you set the value to 0 over all the other axis

answered May 30, 2018 at 15:14

Ben.T

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1 Comment

Abhay Gupta Over a year ago

The axis and index are calculated by a program in my case. For your method to work, one needs to know them beforehand.

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