Re: [Numpy-discussion] Is there a defined way to "unpad" an array, and if not, should there be?
It is great to hear that this might be useful. I would LOVE to create a PR on this idea and contribute back to numpy...but let's not get ahead of ourselves :-) Regarding the name, I kinda like "unpad" since it relates directly to "pad", analogous to "ravel" and "unravel" for instance. Or maybe "depad". Although, it's possible to use this on any array, not just a previously padded one, so maybe tying it too directly to "pad" is not right, in which case "trim" and "crop" are both perfect. I must admit that I find it odd that these functions are not in numpy already. I just searched the docs and they show up as keyword args for a few functions but are otherwise conspicuously absent. Also, funnily, there is a link to "padding arrays" but it is basically empty: https://numpy.org/doc/stable/reference/routines.padding.html. Alternatively, I don't hate the idea of passing negative pad widths into "pad". I actually tried this at one point to see if there was a hidden functionality there, to no avail. BTW, we just adding a custom "unpad" function to our PoreSpy package for this purpose: https://github.com/PMEAL/porespy/blob/dev/porespy/tools/_unpadfunc.py On Mon, Apr 12, 2021 at 9:15 PM Stephan Hoyer wrote: > On Mon, Apr 12, 2021 at 5:12 PM Jeff Gostick wrote: > >> I guess I should have clarified that I was inquiring about proposing a >> 'feature request'. The github site suggested I open a discussion on this >> list first. There are several ways to effectively unpad an array as has >> been pointed out, but they all require more than a little bit of thought >> and care, are dependent on array shape, and honestly error prone. It would >> be very valuable to me to have such a 'predefined' function, so I was >> wondering if (a) I was unaware of some function that already does this and >> (b) if I'm alone in thinking this would be useful. >> > > Indeed, this is a fair question. > > Given that this is not entirely trivial to write correctly, I think it > would be reasonable to add the inverse operation for pad() into NumPy. This > is generally better than encouraging users to write their own thing. > > From a naming perspective, here are some possibilities: > unpad > trim > crop > > I think "trim" would be pretty descriptive, probably slightly better than > "unpad." > ___ > NumPy-Discussion mailing list > NumPy-Discussion@python.org > https://mail.python.org/mailman/listinfo/numpy-discussion > ___ NumPy-Discussion mailing list NumPy-Discussion@python.org https://mail.python.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] Is there a defined way to "unpad" an array, and if not, should there be?
I guess I should have clarified that I was inquiring about proposing a 'feature request'. The github site suggested I open a discussion on this list first. There are several ways to effectively unpad an array as has been pointed out, but they all require more than a little bit of thought and care, are dependent on array shape, and honestly error prone. It would be very valuable to me to have such a 'predefined' function, so I was wondering if (a) I was unaware of some function that already does this and (b) if I'm alone in thinking this would be useful. On Mon, Apr 12, 2021 at 7:42 PM Aaron Meurer wrote: > On Mon, Apr 12, 2021 at 2:29 PM Stephan Hoyer wrote: > > > > The easy way to unpad an array is by indexing with slices, e.g., > x[20:-4] to undo a padding of [(20, 4)]. Just be careful about unpadding > "zero" elements on the right hand side, because Python interprets an ending > slice of zero differently -- you need to write something like x[20:] to > undo padding by [(20, 0)]. > > You can use x[20:x.shape[0] - 4] to avoid this inconsistency. Or > construct the slice based on the original unpadded shape > (x[20:20+orig_x.shape[0]]). > > Aaron Meurer > > > > > > > On Mon, Apr 12, 2021 at 1:15 PM Jeff Gostick wrote: > >> > >> I often find myself padding an array to do some processing on it (i.e. > to avoid edge artifacts), then I need to remove the padding. I wish there > was either a built in "unpad" function that accepted the same arguments as > "pad", or that "pad" accepted negative numbers (e.g [-20, -4] would undo a > padding of [20, 4]). This seems like a pretty obvious feature to me so > maybe I've just missed something, but I have looked through all the open > and closed issues on github and don't see anything related to this. > >> > >> > >> Jeff G > >> > >> ___ > >> NumPy-Discussion mailing list > >> NumPy-Discussion@python.org > >> https://mail.python.org/mailman/listinfo/numpy-discussion > > > > ___ > > NumPy-Discussion mailing list > > NumPy-Discussion@python.org > > https://mail.python.org/mailman/listinfo/numpy-discussion > ___ > NumPy-Discussion mailing list > NumPy-Discussion@python.org > https://mail.python.org/mailman/listinfo/numpy-discussion > ___ NumPy-Discussion mailing list NumPy-Discussion@python.org https://mail.python.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] Is there a defined way to "unpad" an array, and if not, should there be?
It's definitely just "slicing", but it's a bit inconvenient. I'm thinking more like: arr = np.random.rand(10, 10, 10) W = [[3, 2], [4, 6]] # or W = 4, or W = [4, 5] arr_padded = np.pad(arr, pad_width=W) < Do some stuff to arr_padded > arr = np.unpad(arr_padded, pad_width=W) # Using W just works, no matter how odd the various pad widths were On Mon, Apr 12, 2021 at 4:29 PM Stephan Hoyer wrote: > The easy way to unpad an array is by indexing with slices, e.g., x[20:-4] > to undo a padding of [(20, 4)]. Just be careful about unpadding "zero" > elements on the right hand side, because Python interprets an ending slice > of zero differently -- you need to write something like x[20:] to undo > padding by [(20, 0)]. > > > On Mon, Apr 12, 2021 at 1:15 PM Jeff Gostick wrote: > >> I often find myself padding an array to do some processing on it (i.e. to >> avoid edge artifacts), then I need to remove the padding. I wish there >> was either a built in "unpad" function that accepted the same arguments as >> "pad", or that "pad" accepted negative numbers (e.g [-20, -4] would undo a >> padding of [20, 4]). This seems like a pretty obvious feature to me so >> maybe I've just missed something, but I have looked through all the open >> and closed issues on github and don't see anything related to this. >> >> >> Jeff G >> >> ___ >> NumPy-Discussion mailing list >> NumPy-Discussion@python.org >> https://mail.python.org/mailman/listinfo/numpy-discussion >> > ___ > NumPy-Discussion mailing list > NumPy-Discussion@python.org > https://mail.python.org/mailman/listinfo/numpy-discussion > ___ NumPy-Discussion mailing list NumPy-Discussion@python.org https://mail.python.org/mailman/listinfo/numpy-discussion
[Numpy-discussion] Is there a defined way to "unpad" an array, and if not, should there be?
I often find myself padding an array to do some processing on it (i.e. to avoid edge artifacts), then I need to remove the padding. I wish there was either a built in "unpad" function that accepted the same arguments as "pad", or that "pad" accepted negative numbers (e.g [-20, -4] would undo a padding of [20, 4]). This seems like a pretty obvious feature to me so maybe I've just missed something, but I have looked through all the open and closed issues on github and don't see anything related to this. Jeff G ___ NumPy-Discussion mailing list NumPy-Discussion@python.org https://mail.python.org/mailman/listinfo/numpy-discussion
