match.call with default arguments

Question

As part of a function, I want to output a list of all the arguments and their values, including the default values. For example, a function with these arguments:

<         


        

Answer 1

Hopefully, this doesn't lead to dragons.

foo <- function(x=NULL,y=NULL,z=2) {
  mget(names(formals()),sys.frame(sys.nframe()))

}

foo(x=4)

$x
[1] 4

$y
NULL

$z
[1] 2

print(foo(x=4))

$x
[1] 4

$y
NULL

$z
[1] 2

Answer 2

 foo <- function(x=NULL,y=NULL,z=2) {
   X <- list(x,y,z); names(X) <- names(formals()); X
 }
 z <- foo(4)
 z
#------
$x
[1] 4

$y
NULL

$z
[1] 4

Answer 3

you can use a mix of the 2 , match.call and formals

foo <- function(x=NULL,y=NULL,z=2)
{
  ll <- as.list(match.call())[-1]     ## 
  myfor <- formals(foo)               ## formals with default arguments
  for ( v in names(myfor)){
             if (!(v %in% names(ll)))
                ll <- append(ll,myfor[v])  ## if arg is missing I add it
             }
  ll
}

For example :

  foo(y=2)
$y
[1] 2

$x
NULL

$z
[1] 2

> foo(y=2,x=1)
$x
[1] 1

$y
[1] 2

$z
[1] 2

Answer 4

Here is an attempt to wrap this logic in a reusable function to drop in instead of match.call:

match.call.defaults <- function(...) {
  call <- evalq(match.call(expand.dots = FALSE), parent.frame(1))
  formals <- evalq(formals(), parent.frame(1))

  for(i in setdiff(names(formals), names(call)))
    call[i] <- list( formals[[i]] )


  match.call(sys.function(sys.parent()), call)
}

It looks like it works:

foo <- function(x=NULL,y=NULL,z=2,...) {
  match.call.defaults()
}


> foo(nugan='hand', x=4)
foo(x = 4, y = NULL, z = 2, ... = pairlist(nugan = "hand"))