[Numpy-discussion] Medians that ignore values

David Cournapeau david@ar.media.kyoto-u.ac...
Sun Sep 21 01:56:38 CDT 2008


David Cournapeau wrote:
> Anne Archibald wrote:
>> If users are concerned about performance, it's worth noting that on
>> some machines nans force a fallback to software floating-point
>> handling, with a corresponding very large performance hit. This
>> includes some but not all x86 (and I think x86-64) CPUs. How this
>> compares to the performance of masked arrays is not clear.
>
> I spent some time on this. In particular, for max.min, I did the
> following for the core loop (always return nan if nan is in the array):
>
>  /* nan + x and x + nan are nan, where x can be anything:
> normal,                
>   * denormal, nan, infinite
> */                                                   
>   tmp = *((@typ@ *)i1) + *((@typ@
> *)i2);                                          
>   if(isnan(tmp))
> {                                                                
>             *((@typ@ *)op) =
> tmp;                                                       
>   } else
> {                                                                        
>             *((@typ@ *)op)=*((@typ@ *)i1) @OP@ *((@typ@ *)i2) ? *((@typ@
> *)i1) : *((@typ@ *)i2);
>   }

Grr, sorry for the mangling:

/* nan + x and x + nan are nan, where x can be anything: normal,
 * denormal, nan, infinite */
tmp = *((@typ@ *)i1) + *((@typ@*)i2);
if(isnan(tmp)) {
    *((@typ@ *)op) = tmp;
} else {
    *((@typ@ *)op) = *((@typ@ *)i1) @OP@ *((@typ@ *)i2) ? *((@typ@*)i1) : *((@typ@ *)i2);
}

cheers,

David


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