[R] max and pmax of NA and NaN

peter dalgaard 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)
>> [1] NA
>>> max(NaN, NA)
>> [1] NA
>>> pmax(NaN, NA)
>> [1] NA
>>> pmax(NA, NaN)
>> [1] 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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Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
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Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com

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