[Numpy-discussion] Add sliding_window_view method to numpy

Fri Nov 6 04:45:42 EST 2020

Hi all,

I have absolutely no problem keeping this out of the main namespace.

In fact I'd like to point out that it was not my idea. Rather, it was
proposed by Bas van Beek in the comments [1,2] and received a little
more scrutiny from Eric Wieser in [3].

The reason that it didn't receive the scrutiny it probably deserves is
that it got a bit mangled up with the array dispatch discussion; sorry
for that.

On the subject matter, I am also curious about the potential for
confusion. What other behavior could one expect from a sliding window
view with this shape?

As I said, I am completely fine with keeping this out of the main
namespace, but I agree with Sebastian's comment, that
`np.lib.stride_tricks` is perhaps not the best namespace. The reason
from my point of view is that stride tricks is really a technical (and
slightly ominous) name that might throw of more application oriented
programmers from finding and using this function. Thinking of my
scientist colleagues, I think those are exactly the kind of users that
could benefit from such a prototyping tool.

Cheers
Klaus

[1] https://github.com/numpy/numpy/pull/17394#issuecomment-700998618
[2] https://github.com/numpy/numpy/pull/17394#discussion_r498215468
[3] https://github.com/numpy/numpy/pull/17394#discussion_r498724340

On 06/11/2020 01:39, Sebastian Berg wrote:
> On Thu, 2020-11-05 at 17:35 -0600, Sebastian Berg wrote:
>> 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...
> 
> 
> In any case, its the safe bet for NumPy 1.20 at least so I opened a PR:
> 
>     https://github.com/numpy/numpy/pull/17720
> 
> Name changes, etc. are also possible of course.
> 
> I still think it might be nice to find a better place for this type of
> function that `np.lib.stride_tricks` though, but dunno...
> 
> - Sebastian
> 
> 
> 
>>
>> 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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