[R] How to make a function aware of its own call arguments

[Duncan Murdoch]

On 24/03/2016 10:28 AM, sbihorel wrote:
> Hi,
>
> Thanks for your suggestion.
>
> missing(x) works only if x is not altered within the function, which is
> not the case in my actual function (which is more complex than the
> example function I send in my previous post).

That's not quite true:  missing(x) works *before* x is altered within 
the function.  It works even if x has a default value.

So your myf2 could just use missing(c):

myf2 <- function(a=1, b=2, fun=NULL, c=myfun1(b,fun)){

    if (myf1(b,fun)>0 && missing(c)){
      c <- b
    }
    print(list(a,b,c))
}


>
> Are you aware of any function what would query the original function
> call arguments no matter what happens in the function?

The match.call() function does that, but I think you don't need that:

f <- function(x = 1, ...) {
   x <- 2
   match.call()
}
f(3)
## Prints:  f(x = 3)

Duncan Murdoch

>
> Sebastien
>
> On 3/24/2016 8:47 AM, Jeff Newmiller wrote:
> > Don't provide a default value for c in the parameter list. Then you
> > can use the missing() function to make decisions, including whether to
> > generate a default value for c or not.
> > --
> > Sent from my phone. Please excuse my brevity.
> >
> > On March 24, 2016 5:11:43 AM PDT, sbihorel
> > <Sebastien.Bihorel at cognigencorp.com> wrote:
> >
> >     Hi,
> >
> >     Please consider the following functions:
> >
> >     myf1 <- function(x,fun){
> >         if (is.null(fun)){
> >           x
> >         } else {
> >           do.call(fun, list(x))
> >         }
> >     }
> >
> >     myf2 <- function(a=1, b=2, fun=NULL, c=myfun1(b,fun)){
> >
> >         if (myf1(b,fun)>0 & <c was not provided in function call>){
> >           c <- b
> >         }
> >         print(list(a,b,c))
> >     }
> >
> >     myf2(a=2,b=3,fun=exp)
> >     myf2(a=2,b=3,fun=exp,c=4)
> >
> >     I need to replace "<c was not provided in function call>" by some code
> >     that would make myf2 aware of it own calls and of the fact that the c
> >     argument was provided or not in the function calls.
> >
> >     Thanks for your help
> >
> >     Sebastien
> >
> >     ------------------------------------------------------------------------
> >
> >     R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see
> >     https://stat.ethz.ch/mailman/listinfo/r-help
> >     PLEASE d
> >       o read
> >     the posting guidehttp://www.R-project.org/posting-guide.html
> >     and provide commented, minimal, self-contained, reproducible code.
> >
> -- Sebastien Bihorel Associate Director, Pharmacometrics Buffalo Office:
> +1-716-633-3463 ext. 323 | Website <http://www.cognigencorp.com>
> <http://www.simulations-plus.com/Default.aspx>
>
> ______________________________________________
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> and provide commented, minimal, self-contained, reproducible code.