R help - Jan 2018 - max and pmax of NA and NaN

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.

------------------
>>>>> 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

> 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.

-pd
> 
> ------------------
>>>>>> 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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