Duplicate after every row and column in numpy array

Question

I have the following array:

first = array([[4, 5],
               [7, 9]])

And I would like to duplicate every element i into every following i + 1 row and i + 1 column.

My output should look like this:

array([[4, 4, 5, 5],
       [4, 4, 5, 5],
       [7, 7, 9, 9],
       [7, 7, 9, 9]])

I can't think of any clever way without doing it element by element, taking first[0,0} * np.ones((2,2)) and concatenating the results. — Tim Roberts
– Tim Roberts, Commented Jan 27, 2022 at 22:48

user17242583 · Accepted Answer · 2022-01-27 22:57:13Z

2

Just repeat twice:

>>> first.repeat(2, axis=1).repeat(2, axis=0)
array([[4, 4, 5, 5],
       [4, 4, 5, 5],
       [7, 7, 9, 9],
       [7, 7, 9, 9]])

Slightly more compact:

first.repeat(2,1).repeat(2,0)

answered Jan 27, 2022 at 22:57

user17242583

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Comments

ti7 · Accepted Answer · 2022-01-31 15:13:47Z

You can use scipy.ndimage.zoom with the order set to 0 to keep replicating your array

>>> arr
array([[4, 5],
       [7, 9]])
>>> scipy.ndimage.zoom(arr, 2, order=0)
array([[4, 4, 5, 5],
       [4, 4, 5, 5],
       [7, 7, 9, 9],
       [7, 7, 9, 9]])

zoom also works with greater values and/or can approximate to floats (zooming in or out) and in different scales by-axis (including higher dimensions)

>>> scipy.ndimage.zoom(arr, 5, order=0)
array([[4, 4, 4, 4, 4, 5, 5, 5, 5, 5],
       [4, 4, 4, 4, 4, 5, 5, 5, 5, 5],
       [4, 4, 4, 4, 4, 5, 5, 5, 5, 5],
       [4, 4, 4, 4, 4, 5, 5, 5, 5, 5],
       [4, 4, 4, 4, 4, 5, 5, 5, 5, 5],
       [7, 7, 7, 7, 7, 9, 9, 9, 9, 9],
       [7, 7, 7, 7, 7, 9, 9, 9, 9, 9],
       [7, 7, 7, 7, 7, 9, 9, 9, 9, 9],
       [7, 7, 7, 7, 7, 9, 9, 9, 9, 9],
       [7, 7, 7, 7, 7, 9, 9, 9, 9, 9]])
>>> scipy.ndimage.zoom(arr, 0.5, order=0)
array([[4]])
>>> scipy.ndimage.zoom(arr, (2,3), order=0)
array([[4, 4, 4, 5, 5, 5],
       [4, 4, 4, 5, 5, 5],
       [7, 7, 7, 9, 9, 9],
       [7, 7, 7, 9, 9, 9]])

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