[Numpy-discussion] Medians that ignore values
David Cournapeau
david@ar.media.kyoto-u.ac...
Fri Sep 19 04:20:56 CDT 2008
Stéfan van der Walt wrote:
>
> So am I. In all my use cases, NaNs indicate trouble.
Yes, so I would like to have the opinion of people with other usage
than ours.
>
> Because we have x.max() silently ignoring NaNs, which causes a lot of
> head-scratching, swearing and failed experiments.
But cannot this be fixed at the python level of the max function ? I
think it is expected to have the low level C functions to ignore/be
bogus if you have Nan. After all, if you use sort of the libc with nan,
or sort in C++ for a vector of double, it will not work either.
But on my numpy, it looks like nan breaks min/max, they are not ignored:
np.min(np.array([0, np.nan, 1]))
-> 1.0 # bogus
np.min(np.array([0, np.nan, 2]))
-> 2.0 # ok
np.min(np.array([0, np.nan, -1]))
-> -1.0 # ok
np.max(np.array([0, np.nan, -1]))
> -1.0 # bogus
Which only makes sense when you guess how they are implemented in C...
cheers,
David
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