R help - Mar 2010 - Dealing with an argument missing in ...

Hi the list

I define a S3 function that can have a various number of argument using 
'...'
When some arguments are missing, I would like to give them some default 
value:
 
func.numeric <- function(x,...){
   if(missing(y)){y<-3}
}
 
But it does not works...
 
I precise that I can not put 'y' explicitly in the argument list since 
func is an S3 function, I cannot change its arguments.
Any suggestions?
 
Thanks
Christophe

On Wed, 10 Mar 2010, Christophe Genolini wrote:
> Hi the list
>
> I define a S3 function that can have a various number of argument using
'...'
> When some arguments are missing, I would like to give them some default 
> value:
>
> func.numeric <- function(x,...){
>  if(missing(y)){y<-3}
> }
>
> But it does not works...
>
> I precise that I can not put 'y' explicitly in the argument list
since func
> is an S3 function, I cannot change its arguments.
> Any suggestions?
If the generic func() has arguments "x" and "...", then you
can easily
define a method func.numeric(x, y, ...). Methods need to implement all 
arguments of a generic (including ...) but may add additional argument.

hth,
Z
> Thanks
> Christophe
>
> ______________________________________________
> R-help at r-project.org 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 Wed, 2010-03-10 at 11:28 +0100, Christophe Genolini
wrote:
> Hi the list
> 
> I define a S3 function that can have a various number of argument using 
> '...'
> When some arguments are missing, I would like to give them some default 
> value:
>  
> func.numeric <- function(x,...){
>    if(missing(y)){y<-3}
> }
>  
> But it does not works...
If you don't want to specify the extra arguments for some reason in this
method, then you can process the '...'

func.numeric <- function(x, ...) {
    dots <- list(...)
    if(!("y" %in% names(dots))) {
        y <- 3
    } else {
        y <- dots[["y"]]
    }
    return(x + y)
}
> func.numeric(x = 3)
[1] 6
> func.numeric(x = 3, y = 10)
[1] 13
> I precise that I can not put 'y' explicitly in the argument list
since
> func is an S3 function, I cannot change its arguments.
You can, as long as you include all the arguments of the generic:

foo <- function(x, ...) {
    UseMethod("foo")
}

foo.numeric <- function(x, y, ...) {
    return(x + y)
}
> foo(x = 3, y = 10)
[1] 13

HTH

G
> Any suggestions?
>  
> Thanks
> Christophe
> 
> ______________________________________________
> R-help at r-project.org 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.
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