[Rd] Is it possible to define a function's arguments via a wildcard in 'substitute()'?

[Hadley Wickham]

I think for the case where you want to built up a call from a function
name + list of arguments, it's best to use call or as.call:

call("f", a = 1, b = 2, c = 3)

or if you already have the list:
l <- list(as.name("f"), a = 1, b = 2, c = 3)
as.call(l)

Hadley

On Thu, May 26, 2011 at 10:15 AM, Janko Thyson
<janko.thyson.rstuff at googlemail.com> wrote:
> Dear List,
>
> just out of pure curiosity: is it possible to define a function via
> 'substitute()' such that the function's formal arguments are specified by a
> "wildcard" that is substituted when the expression is evaluated?
>
> Simple example:
>
> x.args <- formals("data.frame")
> x.body <- expression(
>    out <- myArg + 100,
>    return(out)
> )
>
> expr <- substitute(
>    myFoo <- function(
>        ARGS,
>        myArg
>    ){
>        print("hello world!")
>        print(ARGS)
>        eval(BODY)
>
>    },
>    list(ARGS=x.args, BODY=x.body)
> )
>
> eval(expr)
> myFoo(myArg=5)
> # works
>
> myFoo(a=1:3, stringsAsFactors=FALSE, myArg=5)
> # does not work
>
> It works for wildcard 'BODY' in the function's body, but not for wildcard
> 'ARGS' in the argument definition part of the function definition.
>
> I thought that when writing a function that depends on some other function
> like 'data.frame()', it would maybe be possible not to 'hardcode' the formal
> arguments of 'data.frame()' in the new function def but to have it mapped
> somewhat dynamically so that when 'data.frame()' changes, the new function
> would change as well. This is probably a bad idea for countless reasons,
> nevertheless I'd be interested in learning if it's possible at all ;-)
>
> TIA,
> Janko
>
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>



-- 
Assistant Professor / Dobelman Family Junior Chair
Department of Statistics / Rice University
http://had.co.nz/