R help - Feb 2008 - matching last argument in function

I often want to temporarily modify the options() options, e.g.

a <- seq(10000001, 10000001 + 10) # some wide object

with.options <- function(..., expr) {
  options0 <- options(...)
  tryCatch(expr, finally=options(options0))
}

Then I can use:

with.options(width=160, expr = print(a))

But I'd like to avoid explicitly naming the expr argument, as in:

with.options(width=160, print(a))

How can I do this with R's argument matching? (I prefer the expr as
the last argument since it could be a long code block. Also, I'd like
with.options to take multiple options.)

TIA

Alistair -

I don't believe this is possible.  The only way formal arguments (like 
expr) can be matched after a '...' is with *exact* name matching.  Why 
do you want to avoid explicitly naming the expr argument?

If you always want the expr argument last, you might be able to just use 
... as the sole argument to your function, and strip off the last 
element inside the function as 'expr', and use all but the last element 
as your list of options.  This requires that expr always be given last 
though.  Probably best just to explicitly name the expr argument.

Erik Iverson

Alistair Gee wrote:
> I often want to temporarily modify the options() options, e.g.
> 
> a <- seq(10000001, 10000001 + 10) # some wide object
> 
> with.options <- function(..., expr) {
>   options0 <- options(...)
>   tryCatch(expr, finally=options(options0))
> }
> 
> Then I can use:
> 
> with.options(width=160, expr = print(a))
> 
> But I'd like to avoid explicitly naming the expr argument, as in:
> 
> with.options(width=160, print(a))
> 
> How can I do this with R's argument matching? (I prefer the expr as
> the last argument since it could be a long code block. Also, I'd like
> with.options to take multiple options.)
> 
> TIA
> 
> ______________________________________________
> 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 Tue, 12 Feb 2008, Alistair Gee wrote:
> I often want to temporarily modify the options() options, e.g.
>
> a <- seq(10000001, 10000001 + 10) # some wide object
>
> with.options <- function(..., expr) {
>  options0 <- options(...)
>  tryCatch(expr, finally=options(options0))
> }
>
> Then I can use:
>
> with.options(width=160, expr = print(a))
>
> But I'd like to avoid explicitly naming the expr argument, as in:
>
> with.options(width=160, print(a))
>
> How can I do this with R's argument matching?
You can't.  You could provide a list, though:

with.options <- function(optionlist,expr){
   option0<-options(optionlist)
   on.exit(options(options0))
   eval.parent(expr)
}

then 
with.options(width=160, print(a))
with.options(list(width=160, warn=1), print(a))


        -thomas

Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle

Try this:

with.options <- function(...) {
    L <- as.list(match.call())[-1]
    len <- length(L)
    old.options <- do.call(options, L[-len])
    on.exit(options(old.options))
    invisible(eval.parent(L[[len]]))
}
> with.options(width = 40, print(1:25))
 [1]  1  2  3  4  5  6  7  8  9 10 11 12
[13] 13 14 15 16 17 18 19 20 21 22 23 24
[25] 25
> with.options(width = 80, print(1:25))
 [1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25




On Feb 12, 2008 12:45 PM, Alistair Gee <alistair.gee at gmail.com>
wrote:
> I often want to temporarily modify the options() options, e.g.
>
> a <- seq(10000001, 10000001 + 10) # some wide object
>
> with.options <- function(..., expr) {
>  options0 <- options(...)
>  tryCatch(expr, finally=options(options0))
> }
>
> Then I can use:
>
> with.options(width=160, expr = print(a))
>
> But I'd like to avoid explicitly naming the expr argument, as in:
>
> with.options(width=160, print(a))
>
> How can I do this with R's argument matching? (I prefer the expr as
> the last argument since it could be a long code block. Also, I'd like
> with.options to take multiple options.)
>
> TIA
>
> ______________________________________________
> 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.
>