R help - Nov 2006 - writing function with ,... )

Hi to all
I did not found the right hints for functions with the dot-dot-dot argument.
Is it possible to write own functions with the tree dots and if yes 
what's wrong with the following example?


test <- function(x, ...)
{
print (x)
if (exists("y"))print(y)
if (exists("z"))print(z)
}

test(4,y=2)

With regards Carmen

Try this:
> test <- function(x, ...) {
+ print(x)
+ dots <- list(...)
+ if ("y" %in% names(dots)) print(dots$y)
+ }
> test(3, y = 43)
[1] 3
[1] 43
> test(4, z = 44)
[1] 4
>
On 11/30/06, Carmen Meier <carmei3 at web.de>
wrote:
> Hi to all
> I did not found the right hints for functions with the dot-dot-dot
argument.
> Is it possible to write own functions with the tree dots and if yes
> what's wrong with the following example?
>
>
> test <- function(x, ...)
> {
> print (x)
> if (exists("y"))print(y)
> if (exists("z"))print(z)
> }
>
> test(4,y=2)
>
> With regards Carmen
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

On Thu, 2006-11-30 at 21:10 +0100, Carmen Meier wrote:
> Hi to all
> I did not found the right hints for functions with the dot-dot-dot
argument.
> Is it possible to write own functions with the tree dots and if yes 
> what's wrong with the following example?
> 
> 
> test <- function(x, ...)
> {
> print (x)
> if (exists("y"))print(y)
> if (exists("z"))print(z)
> }
> 
> test(4,y=2)
> 
> With regards Carmen
 
Carmen,

The problem is that 'y' and 'z' don't exist as R objects, so
the result
of both tests is FALSE.

Try this:

test <- function(x, ...)
{
  print(x)
  dotargs <- list(...)
  if ("y" %in% names(dotargs)) print(dotargs$y)
  if ("z" %in% names(dotargs)) print(dotargs$z)
}
> test(4)
[1] 4
> test(4, y = 2)
[1] 4
[1] 2
> test(4, y = 2, z = 3)
[1] 4
[1] 2
[1] 3

HTH,

Marc Schwartz

Thanks, a lot
I was not able to find it the hole day ...
Carmen

Phil Spector schrieb:
> Carmen -
>    You certainly can write functions that use ..., but you need
> to extract the arguments that the dots represent with list().
> Here's a modified version of your function that may help explain
> how this feature works.
>
> test <- function(x,...){
>     print(x)
>     args = list(...)
>     if('y' %in% names(args))print(args$y)
>     if('z' %in% names(args))print(args$z)
> }
>
>                                        - Phil Spector
>                      Statistical Computing Facility
>                      Department of Statistics
>                      UC Berkeley
>                      spector at stat.berkeley.edu
>
>