[Numpy-discussion] What should be the value of nansum of nan's?

[Travis Oliphant]

On Apr 26, 2010, at 12:03 PM, Charles R Harris wrote:

>
>
> On Mon, Apr 26, 2010 at 10:55 AM, Charles R Harris <charlesr.harris at gmail.com 
> > wrote:
> Hi All,
>
> We need to make a decision for ticket #1123 regarding what nansum  
> should return when all values are nan. At some earlier point it was  
> zero, but currently it is nan, in fact it is nan whatever the  
> operation is. That is consistent, simple and serves to mark the  
> array or axis as containing all nans. I would like to close the  
> ticket and am a bit inclined to go with the current behaviour  
> although there is an argument to be made for returning 0 for the  
> nansum case. Thoughts?
>
>
> To add a bit of context, one could argue that the results should be  
> consistent with the equivalent operations on empty arrays and always  
> be non-nan.
>
> In [1]: nansum([])
> Out[1]: nan
>
> In [2]: sum([])
> Out[2]: 0.0


I favor nansum([])  returning 0.0 which implies returning 0.0 when all  
the elements are nan.

-Travis





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