Combine multiple arrays into a single nested array in Python

Question

I would like to combine N arrays of shape (I, J) into a single array of shape (I, J, N) such that the value at (i, j, n) in the final array is equal to the value of the n-th array at (i, j).

For example, let's say I have two arrays:

arr1 = [[2,3,4],
        [3,4,5]]

arr2 = [[3,4,2],
         [4,3,5]]

Then the final array would look like:

arr_final == [[[2,3], [3,4], [4,2]], 
              [[3,4], [4,3], [5,5]]]

Or, to take a more straightforward example:

arr1 = [[0,0,0],
        [0,0,0]]

arr2 = [[1,1,1],
         [1,1,1]]

arr3 = [[2,2,2],
         [2,2,2]]

Then the final array would look like:

arr_final == [[[0,1,2], [0,1,2], [0,1,2]], 
              [[0,1,2], [0,1,2], [0,1,2]]]

Is there a function in Python, or more specifically Numpy, that could help me with this?

What does np.array((arr1, arr2)) produce? A (2,i,j)? That's the usual way of combining N arrays. — hpaulj
– hpaulj, Commented Jan 25, 2023 at 19:29

juanpethes · Accepted Answer · 2023-01-25 17:56:38Z

1

In Numpy, you can use numpy.stack. Remember to specify the axis as -1 in order to get it to correctly compose it as you want according to your question.

import numpy as np

arr_final = np.stack([arr1, arr2, ..., arrN], axis=-1)

will produce the desired outcome.

answered Jan 25, 2023 at 17:56

juanpethes

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