Good ways to “expand” a numpy ndarray?

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You can use numpy.pad, as follows:

>>> import numpy as np
>>> a=[[1,2],[3,4]]
>>> np.pad(a, ((0,0),(0,3)), mode="constant", constant_values=0)
array([[1, 2, 0, 0, 0],
       [3, 4, 0, 0, 0]])

Here np.pad says, “Take the array a and add 0 rows above it, 0 rows below it, 0 columns to the left of it, and 3 columns to the right of it. Fill these columns with a constant specified by constant_values“.

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