[R] Retrieve ... argument values

[Simon Fear]

For most purposes a more useful technique is to write the
function with a default NULL argument

myfunc <- function(x, ylim=NULL)

so that it can be called as myfunc(x) or myfunc(x,y). Inside
the function you test for !is.null(ylim) and take appropriate
action.

Alternatively, and maybe more commonly, you give ylim a 
sensible default so the caller has to be explicit about 
setting ylim to NULL if required.

As it happens, in your specific case you can write as you did except
for the pseudo-line(hasArg(ylim)), because all arguments will get
passed to plot, which will itself recognise and test for
an argument called ylim, within its own "...".

HTH

> -----Original Message-----
> From: huan.huang at bnpparibas.com [mailto:huan.huang at bnpparibas.com]
> Sent: 16 September 2003 15:14
> To: r-help at stat.math.ethz.ch
> Subject: [R] Retrieve ... argument values
> 
> 
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> 
> Dear R users,
> 
> I want to retrieve "..." argument values within a function. Here is a
> small
> exmaple:
> 
> myfunc <- function(x, ...)
> {
>       if (hasArg(ylim))  a <- ylim
>       plot(x, ...)
> }
> 
> x <- rnorm(100)
> myfunc(x, ylim=c(-0.5, 0.5))
> Error in myfunc(x, ylim = c(-0.5, 0.5)) : Object "ylim" not found
> >
> 
> I need to retrieve values of "ylim" (if it is defined when function is
> called) for later use in the function. Can anybody give me some hint?
> 
> Thanks a lot.
> 
> Huan
> 
> 
> 
> 
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Simon Fear
Senior Statistician
Syne qua non Ltd
Tel: +44 (0) 1379 644449
Fax: +44 (0) 1379 644445
email: Simon.Fear at synequanon.com
web: http://www.synequanon.com
 
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