ENH: np.roll: extra argument to pad with zeros or constant

[josephernest]

Proposed new feature or change:

In many situations, it is required to shift an array (like np.roll) and fill the values with zeros, instead of making the array "loop".

Is there a way to implement this:

x = np.array([1, 2, 3, 4, 5]
np.roll(x, 2, method="constant")   #  [ 0 0 1 2 3 ]   instead of  [ 4 5 1 2 3 ]
np.roll(x, -2, method="constant")  #  [ 3 4 5 0 0 ]  instead of   [ 3 4 5 1 2 ]

?

Example : python numpy roll with padding

Important notes:

• solutions with np.pad exist but are slower, see https://stackoverflow.com/questions/2777907/python-numpy-roll-with-padding#comment3270288_3153267

• other people have the needs for this: https://stackoverflow.com/questions/2777907/python-numpy-roll-with-padding#comment120688507_2778068: I think np.roll should do it natively with a keyword argument. (quite upvoted)

• this solution works: https://stackoverflow.com/a/2778068 but it would be interesting for the Numpy API to have this useful option (in the same way np.pad has constant mode, etc.)

[arararz]

Has this been added yet? If not I can take on this issue

[josephernest]

It would be interesting @arararz, thanks!

[luxedo]

I disagree of this proposal.

The documentation states that:

Roll array elements along a given axis.

Elements that roll beyond the last position are re-introduced at the first.

Furthermore, I think that the name roll is very expressive in it's intent in my opinion.

I'd much prefer the creation of a new function like scipy.ndimage.shift.