[R] pass "..." to multiple sub-functions

[Peter Ruckdeschel]

Dear Baptiste,

> I know I have seen this discussed before but I haven't been successful
> in searching for "ellipsis", "dots", "..." in the archives. I would
> like to filter "..." arguments according to their name, and dispatch
> them to two sub-functions, say fun1 and fun2. I looked at lm() but it
> seemed more complicated than I need as it modifies the calling
> function among other things. What is the best approach for this? My
> current version presented below seems very awkward.
> 
> Best regards,
> 
> baptiste
> 
> sessionInfo()
> R version 2.9.2 (2009-08-24)
> i386-apple-darwin8.11.1
> 
> fun1 <- function(col, row){
>   print(col)
>   print(row)
> }
> 
> fun2 <- function(x){
>   print(x)
> }
> 
> foo <- function(..., lty=1){
> 
>   dots <- list(...)
> 
>   cl <- match.call()
> 
>   col <- eval.parent(cl$col)
>   row <- eval.parent(cl$row)
> 
>   params.fun1 <-  c("col", "row")
> 
>   removed <- na.omit(match(names(cl), params.fun1))
>   # index whichever arguments were passed to fun1
> 
>   fun1(col, row)
> 
>   fun2(dots[seq_along(dots)[-removed]])

Instead of passing all remaining arguments stacked into
one list (= 1 argument x to function fun2) you might want
to be able to retain them as distinct arguments;

so you might want to replace fun2 by

  fun2.a <- function(...) print(list(...))

and the call to fun2 in foo by

  do.call(fun2.a, dots.remaining)

where, sticking to your code, you could obtain
dots.remaining as

   removed <- na.omit(match(names(cl), params.fun1))
   dots.remaining <- dots[seq_along(dots)[-removed]]

or by

   removed <- c("lty",params.fun1)
   ## I assume you do not want to pass on argument "lty"...
   dots.remaining <- cl[-1] ### remove the function name
   dots.remaining <- dots.remaining[! names(dots.remaining)
                             %in% removed]

Best, Peter