[Numpy-discussion] Floating point "close" function?

Olivier Delalleau shish@keba...
Sat Mar 3 12:50:50 CST 2012


Le 3 mars 2012 13:07, Joe Kington <jkington@wisc.edu> a écrit :

>
>
> On Sat, Mar 3, 2012 at 9:26 AM, Robert Kern <robert.kern@gmail.com> wrote:
>
>> On Sat, Mar 3, 2012 at 15:22, Benjamin Root <ben.root@ou.edu> wrote:
>> >
>> >
>> > On Saturday, March 3, 2012, Robert Kern <robert.kern@gmail.com> wrote:
>> >> On Sat, Mar 3, 2012 at 14:31, Ralf Gommers <
>> ralf.gommers@googlemail.com>
>> >> wrote:
>> >>>
>> >>>
>> >>> On Sat, Mar 3, 2012 at 3:05 PM, Robert Kern <robert.kern@gmail.com>
>> >>> wrote:
>> >>>>
>> >>>> On Sat, Mar 3, 2012 at 13:59, Ralf Gommers <
>> ralf.gommers@googlemail.com>
>> >>>> wrote:
>> >>>> >
>> >>>> >
>> >>>> > On Thu, Mar 1, 2012 at 11:44 PM, Joe Kington <jkington@wisc.edu>
>> >>>> > wrote:
>> >>>> >>
>> >>>> >> Is there a numpy function for testing floating point equality that
>> >>>> >> returns
>> >>>> >> a boolean array?
>> >>>> >>
>> >>>> >> I'm aware of np.allclose, but I need a boolean array.  Properly
>> >>>> >> handling
>> >>>> >> NaN's and Inf's (as allclose does) would be a nice bonus.
>> >>>> >>
>> >>>> >> I wrote the function below to do this, but I suspect there's a
>> method
>> >>>> >> in
>> >>>> >> numpy that I missed.
>> >>>> >
>> >>>> >
>> >>>> > I don't think such a function exists, would be nice to have. How
>> about
>> >>>> > just
>> >>>> > adding a keyword "return_array" to allclose to do so?
>> >>>>
>> >>>> As a general design principle, adding a boolean flag that changes the
>> >>>> return type is worse than making a new function.
>> >>>
>> >>>
>> >>> That's certainly true as a general principle. Do you have a concrete
>> >>> suggestion in this case though?
>> >>
>> >> np.close()
>> >>
>> >
>> > When I read that, I mentally think of "close" as in closing a file.  I
>> think
>> > we need a synonym.
>>
>> np.isclose()
>>
>
> Would it be helpful if I went ahead and submitted a pull request with the
> function in my original question called "isclose" (along with a complete
> docstring and a few tests)?
>
> One note:
> At the moment, it deliberately compares NaN's as equal. E.g.
>
>     isclose([np.nan, np.nan], [np.nan, np.nan])
>
> will return:
>
>     [True, True]
>
> This obviously runs counter to the standard way NaN's are handled (and
> indeed the definition of NaN).
>
> However, in the context of a floating point "close to" function, I think
> it makes the most sense.
>
> I've had this sitting around in a small project for awhile now, and it's
> been more useful to have it compare NaN's as "approximately equal" than not
> for my purposes at least.
>
> Nonetheless, it's something that needs additional consideration.
>
> Thanks,
> -Joe
>

It would be confusing if numpy.isclose().all() was different from
numpy.allclose(). That being said, I agree it's useful to have NaNs compare
equal in some cases, maybe it could be a new argument to the function?

-=- Olivier
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