[R] Selective 'expansion' of arguments in a match.call() result ...

[Gabor Grothendieck]

Try this:


# ith arg is expanded if expand[[i]] is TRUE where expand is
# extended to vector of same length as ... .
# default is to expand all args if 1st arg is "character"
example2 <- function(..., expand = is.character(..1)) {
	L <- list(...)
	expand <- rep(expand, length = length(L))
	mc <- match.call()
	mc$expand <- NULL
	for(i in which(expand)) mc[[i+1]] <- L[[i]]
	mc
}

# test
a <- b <- 1
example2(a, b)
d <- "a"
example2(d, b)
example2(a, b, expand = TRUE)
example2(a, b, expand = c(TRUE, FALSE))


On 5/31/07, Roberto Brunelli <brunelli at itc.it> wrote:
> Is it  possible to  write a support  function to  automatize selective
> argument expansion (based on argument  value type) as in the following
> example, in  order  to write  terse  code  even  when there  are  many
> arguments?  Forcing evaluation of all arguments is not a problem ...
>
> ______________________________________________Thanks a lot!__________R_
>
> # When called with document = 1, we have the simple match.call() result,
> # when document =  2 and name is a string, it  is expanded, otherwise it
> # is not
>
> example <- function (name, document = FALSE) {
>
>   print(name)
>
>   if(document == 1) {
>     resh          <- match.call()
>   } else if (document == 2) {
>     resh          <- match.call()
>
>     if(is.character(name)) {
>       resh$name     <- name
>     }
>     resh$document <- document
>   } else {
>     resh <- call("<undef>")
>   }
>
>   resh
> }
>
>  > a <- "Roberto"
>  > b <- 1
>  > example(a, document = 1)
> [1] "Roberto"
> example(name = a, document = 1)
>  > example(a, document = 2)
> [1] "Roberto"
> example(name = "Roberto", document = 2)
>  > example(b, document = 2)
> [1] 1
> example(name = b, document = 2)
>  >
>
> --
>        <r/>
> | Roberto Brunelli - [scientist at  Fondazione Bruno Kessler-irst]
> |           'Home can be anywhere, for it is a part of one's self'
>
> ------------------
> ITC -> dall'1 marzo 2007 Fondazione Bruno Kessler
> ITC -> since 1 March 2007 Fondazione Bruno Kessler
>
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