[SciPy-Dev] np.any(), np.all()

[Dieter Werthmüller]

Thanks Phillip and Benny for your replies.

Yes, I specifically saw the issue you mentioned Benny. It is actually 
from 2010, and was moved to GitHub in 2012. This is why I thought I 
quickly ask on the mailing list if anything happened or is planned in 
this regard, because I imagine that very old issues are easily 
forgotten. It looks like this didn't change in the last 8 years, and 
probably won't in the (near) future. Which is fine, I just wanted to 
check before I search for other solutions.

Thanks,
Dieter


On 04/07/18 02:56, Benny Malengier wrote:
> Sorry, I see you mention that issue. Anyway, I would suggest going for a 
> cython or C workaround at the moment and commenting on the tickets. As 
> Phillip says, a separate method would be needed as any and all do a reduce.
> Some methods like firstnotvalue and firstvalue, returning index of a 
> difference from value or the value, so like 
> https://pypi.org/project/py_find_1st/  mentioned in the ticket.
> 
> For multidim arrays, as this operates on 1D arrays, perhaps the 
> firstvalue applied per axis...
> 
> Op wo 4 jul. 2018 om 09:43 schreef Benny Malengier 
> <benny.malengier at gmail.com <mailto:benny.malengier at gmail.com>>:
> 
>     There is an open issue for this since 2012:
>     https://github.com/numpy/numpy/issues/2269
> 
>     Some python and c solutions are suggested in that thread.
> 
>     Op wo 4 jul. 2018 om 06:44 schreef Phillip Feldman
>     <phillip.m.feldman at gmail.com <mailto:phillip.m.feldman at gmail.com>>:
> 
>         Performing a test (to determine whether the loop should be
>         aborted) after looking at each element would cause `np.any` to
>         run slower if all elements are zero, or if the first non-zero
>         element is near the end of the array.  Possibly a separate
>         method that operates in this fashion is needed?
> 
>         Phillip
> 
> 
>         On Mon, Jul 2, 2018 at 11:03 AM, Dieter Werthmüller
>         <dieter at werthmuller.org <mailto:dieter at werthmuller.org>> wrote:
> 
>             Dear devs,
> 
>             Sorry for posting a numpy-issue on the scipy-list. I am not
>             (yet) subscribed to the numpy list, but I believe that the
>             two community have a big enough overlap so it shouldn't
>             matter too much where I post it.
> 
>             I recently encountered the issue that I found that np.any(x)
>             is sort of veeeery slow for big arrays, even if every
>             element has a non-zero value and I only need a True/False
>             response. So my thinking was that if np.any(x) encounters
>             the first non-zero value it should simply return True, which
>             should take basically no time at all if every element in the
>             array is non-zero.
> 
>             Searching for it I found the following two old issues on numpy:
> 
>             1. https://github.com/numpy/numpy/issues/2269
> 
>             It is an issue from 2010, but got some traffic again in 2016
>             and 2017.
> 
> 
>             2. https://github.com/numpy/numpy/issues/3446
> 
>             This is a related issue from 2013, reporting a potential
>             performance regression between numpy 1.6.2 and 1.7.0, that
>             got some traffic in 2016 again as well.
> 
> 
>             I just wanted to ask about the opinions of devs more
>             familiar with these two functions (np.all(), np.any()).
>             Would there be better ways to check if any element in a big
>             (1D or higher dimensions)-array is non-zero (or the reverse
>             with np.all)?
> 
> 
>             Thanks,
>             Dieter
> 
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