[Numpy-discussion] Add sliding_window_view method to numpy

[Sebastian Berg]

On Thu, 2020-11-05 at 12:51 -0800, Stephan Hoyer wrote:
> On Thu, Nov 5, 2020 at 11:16 AM Ralf Gommers <ralf.gommers at gmail.com>
> wrote:
> 
> > 
> > On Thu, Nov 5, 2020 at 4:56 PM Sebastian Berg <
> > sebastian at sipsolutions.net>
> > wrote:
> > 
> > > Hi all,
> > > 
> > > just a brief note that I merged this proposal:
> > > 
> > >     https://github.com/numpy/numpy/pull/17394
> > > 
> > > adding `np.sliding_window_view` into the 1.20 release of NumPy.
> > > 
> > > There was only one public API change, and that is that the
> > > `shape`
> > > argument is now called `window_shape`.
> > > 
> > > This is still a good time for feedback in case you have a better
> > > idea
> > > e.g. for the function or parameter names.
> > > 
> > 
> > The old PR had this in the lib.stride_tricks namespace. Seeing it
> > in the
> > main namespace is unexpected and likely will lead to
> > issues/questions,
> > given that such an overlapping view is going to do behave in ways
> > the
> > average user will be surprised by. It may also lead to requests for
> > other
> > array/tensor libraries to implement this. I don't see any
> > discussion on
> > this in PR 17394, it looks like a decision by the PR author that no
> > one
> > commented on - reconsider that?
> > 
> > Cheers,
> > Ralf
> > 
> 
> +1 let's keep this in the lib.stride_tricks namespace.
> 

I have no reservations against having it in the main namespace and am
happy either way (it can still be exposed later in any case). It is the
conservative choice and maybe it is an uncommon enough function that it
deserves being a bit hidden...

But I am curious, it sounds like you have both very strong
reservations, and I would like to understand them better.

The behaviour can be surprising, but that is why the default is a read-
only view.  I do not think it is worse than `np.broadcast_to` in this
regard. (It is nowhere near as dangerous as `as_strided`.)

It is true that it is specific to NumPy (memory model). So that is
maybe a good enough reason right now.  But I am not sure that stuffing
things into a pretty hidden `np.lib.*` namespaces is a great long term
solution either. There is very little useful functionality hidden away
in `np.lib.*` currently.

Cheers,

Sebastian

> 
> > 
> > 
> > 
> > > Cheers,
> > > 
> > > Sebastian
> > > 
> > > 
> > > 
> > > On Mon, 2020-10-12 at 08:39 +0000, Zimmermann Klaus wrote:
> > > > Hello,
> > > > 
> > > > I would like to draw the attention of this list to PR #17394
> > > > [1] that
> > > > adds the implementation of a sliding window view to numpy.
> > > > 
> > > > Having a sliding window view in numpy is a longstanding open
> > > > issue
> > > > (cf
> > > > #7753 [2] from 2016). A brief summary of the discussions
> > > > surrounding
> > > > it
> > > > can be found in the description of the PR.
> > > > 
> > > > This PR implements a sliding window view based on stride
> > > > tricks.
> > > > Following the discussion in issue #7753, a first implementation
> > > > was
> > > > provided by Fanjin Zeng in PR #10771. After some discussion,
> > > > that PR
> > > > stalled and I picked up the issue in the present PR #17394. It
> > > > is
> > > > based
> > > > on the first implementation, but follows the changed API as
> > > > suggested
> > > > by
> > > > Eric Wieser.
> > > > 
> > > > Code reviews have been provided by Bas van Beek, Stephen Hoyer,
> > > > and
> > > > Eric
> > > > Wieser. Sebastian Berg added the "62 - Python API" label.
> > > > 
> > > > 
> > > > Do you think this is suitable for inclusion in numpy?
> > > > 
> > > > Do you consider the PR ready?
> > > > 
> > > > Do you have suggestions or requests?
> > > > 
> > > > 
> > > > Thanks for your time and consideration!
> > > > Klaus
> > > > 
> > > > 
> > > > [1] https://github.com/numpy/numpy/pull/17394
> > > > [2] https://github.com/numpy/numpy/issues/7753
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> > > > 
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