Numpy array - duplicating rows and centering columns in a larger array

Question

I have a large number of arrays with dimension 72, x where x is less than 144. I'd like to take these arrays and do two things to them:

Duplicate each row in the original so that there are 144 of them.
Center the arrays horizontally inside a larger 144

The end result is a 144x144 array. I'd like to use numpy and to the greatest extent possible avoid loops ( I can already implement this in loops ). I've searched around but haven't found a neat solution yet.

Thanks,

eumiro · Accepted Answer · 2011-04-21 09:13:04Z

2

Let's take a smaller example:

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

b = np.zeros((4,4))

b[:,1:-1] = np.repeat(a, 2, axis=0)

# returns:

array([[ 0.,  1.,  2.,  0.],
       [ 0.,  1.,  2.,  0.],
       [ 0.,  3.,  4.,  0.],
       [ 0.,  3.,  4.,  0.]])

So for your case:

a = np.arange(5184).reshape(72,72)
b = np.zeros((144,144))
b[36:-36,:] = np.repeat(a, int(144 / a.shape[0]) + 1, axis=1)[:,:144]

edited Apr 21, 2011 at 9:13

answered Apr 21, 2011 at 8:48

eumiro

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1 Comment

Brian Over a year ago

I really appreciate this code, unfortunately in its final form it was a little bit too obscure for me to grok. For that reason I settled on writing the matrices as images and then using ImageMagick:

for f in *.png; do   mogrify -geometry $(file $f | cut -f2 -d, | cut -f1 -dx | tr -d " ")x144! -background black -extent 144x144 -gravity center $f; done

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