[Numpy-discussion] the mean, var, std of empty arrays

Charles R Harris charlesr.harris at gmail.com
Wed Nov 21 21:33:58 EST 2012

Hi Olivier,

Please don't top post, it isn't the custom on this list.

On Wed, Nov 21, 2012 at 7:22 PM, Olivier Delalleau <shish at keba.be> wrote:

> Current behavior looks sensible to me. I personally would prefer no
> warning but I think it makes sense to have one as it can be helpful to
> detect issues faster.
> -=- Olivier
> 2012/11/21 Charles R Harris <charlesr.harris at gmail.com>
>> What should be the value of the mean, var, and std of empty arrays?
>> Currently
>> In [12]: a
>> Out[12]: array([], dtype=int64)
>> In [13]: a.mean()
>> Out[13]: nan
>> In [14]: a.std()
>> Out[14]: nan
>> In [15]: a.var()
>> Out[15]: nan
>> I think the nan comes from 0/0. All of these also raise warnings the
>> first time they are called.
The warnings vary and don't directly give information on the cause, i.e.,
empty arrays. If we do go with warnings I think they should be more

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