[R] max and pmax of NA and NaN
pdalgd at gmail.com
Sat Jan 20 17:50:52 CET 2018
> On 20 Jan 2018, at 07:53 , Suharto Anggono Suharto Anggono via R-help <r-help at r-project.org> wrote:
> Extremes.Rd, that documents 'max' and 'pmax', has this in "Details" section, in the paragraph before the last.
> By definition the min/max of a numeric vector containing an NaN is NaN, except that the min/max of any vector containing an NA is NA even if it also contains an NaN.
...but how do you infer that this applies to pmin/pmax? You may want it to, but it specifically talks about the non-parallel min/max.
>>>>>> Michal Burda <michal.burda at centrum.cz>
>>>>>> on Mon, 15 Jan 2018 12:04:13 +0100 writes:
>> Dear R users, is the following OK?
>>> max(NA, NaN)
>>  NA
>>> max(NaN, NA)
>>  NA
>>> pmax(NaN, NA)
>>  NA
>>> pmax(NA, NaN)
>>  NaN
>> ...or is it a bug?
>> Documentation says that NA has a higher priority over NaN.
> which documentation ??
> [That would be quite a bit misleading I think. So, it should be amended ...]
>> Best regards, Michal Burda
> R's help pages are *THE* reference documentation and they have
> (for a long time, I think) had :
> ?NaN has in its 3rd 'Note:'
> Computations involving ‘NaN’ will return ‘NaN’ or perhaps ‘NA’:
> which of those two is not guaranteed and may depend on the R
> platform (since compilers may re-order computations).
> Similarly, ?NA contains, in its 'Details':
> Numerical computations using ‘NA’ will normally result in ‘NA’: a
> possible exception is where ‘NaN’ is also involved, in which case
> either might result (which may depend on the R platform). ........
> Yes, it is a bit unfortunate that this is platform dependent; if
> we wanted to make this entirely consistent (as desired in a
> perfect world), I'm almost sure R would become slower because
> we'd have to do add some explicit "book keeping" / checking
> instead of relying on the underlying C library code.
> Note that for these reasons, often NaN and NA should not be
> differentiated, and that's reason why using is.na(*) is
> typically sufficient and "best" -- it gives TRUE for both NA and NaN.
> Martin Maechler
> ETH Zurich
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