[Rd] missing() (PR#1096)

ripley@stats.ox.ac.uk ripley@stats.ox.ac.uk
Wed, 19 Sep 2001 16:47:40 +0200 (MET DST)


>From the FAQ:

   * In S, `missing(ARG)' remains `TRUE' if ARG is subsequently modified;
     in R it doesn't.


>From ?missing in 1.3.1:

Details:

     `missing(x)' is only reliable if `x' has not been altered since
     entering the function: in particular it will always be true after
     `x <- match.arg(x)'.

My guess is that whatever you were looking at has been changed in the
current version.


On Wed, 19 Sep 2001 hosking@watson.ibm.com wrote:

> Full_Name: J. R. M. Hosking
> Version: 1.3.0
> OS: Windows 2000
> Submission from: (NULL) (198.81.209.16)
>
>
> R documentation suggests that if a function argument x is omitted,
> missing(x) should return TRUE even if x is subsequently assigned a value.
> This happens in S-plus.  But in R:
>
> > test
> function(x){
> print(missing(x))
> if(missing(x)) x<-0
> print(missing(x))
> invisible()
> }
> > test()
> [1] TRUE
> [1] FALSE
> >
>
>
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-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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