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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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
>
>
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
> r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
> Send "info", "help", or "[un]subscribe"
> (in the "body", not the subject !) To: r-help-request at
stat.math.ethz.ch
>
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>
-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
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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?Yes, or then again, no. You can use the function missing() to test whether an explicit argument was supplied.> > "e" <- function(first,second=first) { > if (all(first == second) & is.complex(first)) {ie if (missing(second)){> return(c(Re(first),Im(first))) > } else { > return (c(Re(first),Re(second))) > } > } >This will not preserve the missingness f<-function(a,b,c,d=c){ e(c,d) } This will work, but not if you modify d before calling e() f<-function(a,b,c,d){ e(c,d) } That's why we often use NULL as the default: "e" <- function(first,second=NULL) { if (is.null(second)){ return(c(Re(first),Im(first))) } else { return (c(Re(first),Re(second))) } } f<-function(a,b,c,d=NULL){ e(c,d) } -thomas -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._