[Numpy-discussion] Behavior of nan{max, min} and nanarg{max, min} for all-nan slices.

Nathaniel Smith njs at pobox.com
Thu Oct 3 15:11:37 EDT 2013

On Thu, Oct 3, 2013 at 7:59 PM, Charles R Harris
<charlesr.harris at gmail.com> wrote:
> <snip>
>> Please, no. It's another thing to remember and another way to shoot
>> yourself in the foot and introduce casual bugs.
>> FWIW, my vote is to raise an error or return a nan, which will likely
>> eventually raise an error. If I have all nans, it's usually the case
>> that something's off, and I'd like to know sooner rather than later.
> Here is what I have currently implemented. First, define an AllNanError
> class AllNanError(ValueError):
>     def __init__(self, msg, result):
>         ValueError.__init__(self, msg)
>         self.result = result
> For nanmax/nanmin/nanargmax/nanargmin this error is raised for all-nan axis
> and the result is attached. The exception can then be caught and the result
> examined. A ValueError is what amax, amin return for empty arrays.
> For nanmax/nanmin the result for an empty slice is nan. For
> argnanmax/argnanmin the result of an empty slice is -1, which is easier to
> read and remember than intp.min. A ValueError is what argmin, argmax
> currently return for empty arrays. Note that both of these functions can
> give wrong results if they contain some min/max values respectively. That is
> an old bug and I haven't fixed it.
> The nanmean/nanvar/nanstd functions currently raise a warning for all-nan
> slices and the result for such is nan. These could also be made to raise an
> error.
> Thoughts?

Is this intended for 1.8 or master?


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