Cleanest way to merge two same-shape arrays in Numpy

Question

We have some arrays of the same shape and want to merge them.

By "merge", I mean output a new array with the sum of each i,j in each of the arrays in each position.

import numpy as np
first = np.array([[1,1],[1,1]])
second = np.array([[2,2],[2,2]])
third = np.array([[3,3],[3,3]])

The result should be:

[[6,6],
[6,6]]

Here's my code...but is there a cleaner way? I can't seem to find a built-in method:

def merge_arrays(arrays):
    output = arrays[0]
    for a in arrays[1:]:
        for i,row in enumerate(a):
            for j,col in enumerate(row):
                output[i,j] += a[i,j]
    return output

merge_arrays([first, second, third])

Joe Kington · Accepted Answer · 2013-06-12 15:10:16Z

4

It's just output = first + second + third or np.sum([first, second, third], axis=0).

answered Jun 12, 2013 at 15:10

Joe Kington

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3 Comments

Klaus-Dieter Warzecha Over a year ago

Damned, you did beat me by seconds since you did know the answer while i had to try it in ipython :D

Joe Kington Over a year ago

@KlausWarzecha - I usually get burned when I don't test things out first! (And I actually did this time, too... Forgot the axis=0 when I first typed it.)

Klaus-Dieter Warzecha Over a year ago

@Joe Kington Yes, i saw you editing while i had the simple addition working and was still stumbling over the syntax of np.sum()

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