R help - May 2007 - Selective 'expansion' of arguments in a match.call() result ...

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

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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