[FIXED] python numpy roll with padding

Issue

I'd like to roll a 2D numpy in python, except that I'd like pad the ends with zeros rather than roll the data as if its periodic.

Specifically, the following code

import numpy as np

x = np.array([[1, 2, 3], [4, 5, 6]])

np.roll(x, 1, axis=1)

returns

array([[3, 1, 2],[6, 4, 5]])

but what I would prefer is

array([[0, 1, 2], [0, 4, 5]])

I could do this with a few awkward touchups, but I'm hoping that there's a way to do it with fast built-in commands.

Thanks

Solution

I don't think that you are going to find an easier way to do this that is built-in. The touch-up seems quite simple to me:

y = np.roll(x,1,axis=1)
y[:,0] = 0

If you want this to be more direct then maybe you could copy the roll function to a new function and change it to do what you want. The roll() function is in the site-packages\core\numeric.py file.

Answered By - Justin Peel