[R] how can a function tell if defaults are used?

[Roger Peng]

Maybe a better way is:

e <- function(first, second) {
  if(missing(second)) 
    return(c(Re(first), Im(first)))
  else
    return(c(Re(first), Re(second)))
}

I'm not sure if this is what you're going for.

-roger
_______________________________
UCLA Department of Statistics
rpeng at stat.ucla.edu
http://www.stat.ucla.edu/~rpeng

On Mon, 22 Apr 2002, Robin Hankin wrote:

> 
> Hello everybody
> 
> 
> Is there a good way for a function to tell whether the caller used the
> defaults?
> 
> I'm writing a little function that may take a pair of real arguments
> or a single complex argument (in which case I want the real and
> imaginary components).
> 
> 
> "e" <-   function(first,second=first) {
>   if (all(first == second) & is.complex(first)) {
>     return(c(Re(first),Im(first)))
>   } else {
>     return (c(Re(first),Re(second)))
>   }
> }
> 
> 
> Thus
> 
> > e(1+5i)
> [1] 1 5
> > e(1,5)
> [1] 1 5
> 
> 
> which is what I want, but what is the best way to test whether the
> second argument is explicitly set by the caller or the default is
> used?  My only idea was to test for first == second but this can't be
> optimal.  Help anyone?
> 
> 
> -- 
> 
> Robin Hankin, Lecturer,
> School of Geographical and Environmental Science
> Private Bag 92019 Auckland
> New Zealand
> 
> r.hankin at auckland.ac.nz
> tel 0064-9-373-7599 x6820; FAX 0064-9-373-7042
> 
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