Get all Parameters as List

Does R provide an object/function/method/keyword to get all function arguments?

Using an example: function(a, b="default", ...) would provide a and b as well as ... within the function environment. Is there a statement similar to list(...) that would also include a and b in the result?

Or put yet another way: a shorthand for list(a=a, b=b, ...), given function(a, b, ...)

One solution is to use:

tempf <- function(a, b = 2, ...) {
    argg <- c(as.list(environment()), list(...))
    print(argg)
}
tempf(1, c = 3)
$a
[1] 1

$b
[1] 2

$c
[1] 3

This creates a named list of the argument values.

I think that you want match.call:

tmpfun <- function(a,b,...) {
print(as.list(match.call()))
print(as.list(match.call(expand.dots=FALSE)))
}
> tmpfun(a=1, b=2, c=3, d=4)
[[1]]
tmpfun

$a
[1] 1

$b
[1] 2

$c
[1] 3

$d
[1] 4

[[1]]
tmpfun

$a
[1] 1

$b
[1] 2

$...
$...$c
[1] 3

$...$d
[1] 4

try args function

What are the arguments for mean function?

> args(mean)
function (x, ...) 
NULL

What about lm function?

    > args(lm)
function (formula, data, subset, weights, na.action, method = "qr", 
    model = TRUE, x = FALSE, y = FALSE, qr = TRUE, singular.ok = TRUE, 
    contrasts = NULL, offset, ...) 
NULL

If you want to get a list of arguments try

as.list(args(lm))

Stumbled upon this question while searching for something related. While I realize that this is several years old, the responses appear unsatisfactory, and there does not appear to be any off-the-shelf solution to the question.

It is possible to make an (inelegant) workaround, using a combination of the formals and environment functions. The example below extracts arguments from the environment using names extracted from formals, then appends the ellipsis-list. If you wish to have the values as they were set at the time of function call, set the orig_values argument to TRUE. The function only includes variables implicitly or explicitly set at function call.

allargs <- function(orig_values = FALSE) {
  # get formals for parent function
  parent_formals <- formals(sys.function(sys.parent(n = 1)))
  
  # Get names of implied arguments
  fnames <- names(parent_formals)
  
  # Remove '...' from list of parameter names if it exists
  fnames <- fnames[-which(fnames == '...')]
  
  # Get currently set values for named variables in the parent frame
  args <- evalq(as.list(environment()), envir = parent.frame())
  
  # Get the list of variables defined in '...'
  args <- c(args[fnames], evalq(list(...), envir = parent.frame()))
  
  
  if(orig_values) {
    # get default values
    defargs <- as.list(parent_formals)
    defargs <- defargs[unlist(lapply(defargs, FUN = function(x) class(x) != "name"))]
    args[names(defargs)] <- defargs
    setargs <- evalq(as.list(match.call())[-1], envir = parent.frame())
    args[names(setargs)] <- setargs
  }
  return(args)
}


tempf <- function(a, b = 2, ...) {
  d <- 5
  b <- 3
  
  cat("Currently set values defined in call or formals\n")
  print(allargs())
  cat("Values as defined at the time of the call\n")
  print(allargs(T))
}

tempf(1, c = 3)

Currently set values defined in call or formals
$a
[1] 1

$b
[1] 3

$c
[1] 3

Values as defined at the time of the call
$a
[1] 1

$b
[1] 2

$c
[1] 3

I believe you are looking for formals:

formals(sd)
$x


$na.rm
[1] FALSE

And using dput on this gives you the form you specify in the question:

dput(formals(sd))
list(x = , na.rm = FALSE)

Note that formals doesn't work for primitive functions, only closures.

rlang::fn_fmls gives a brief and clean solution:

library(ggplot2)
library(rlang)

# action
argument_list <- rlang::fn_fmls(fn = geom_point)

# evaluate output
class(argument_list)
#> [1] "pairlist"

is.list(argument_list)
#> [1] TRUE

argument_list
#> $mapping
#> NULL
#> 
#> $data
#> NULL
#> 
#> $stat
#> [1] "identity"
#> 
#> $position
#> [1] "identity"
#> 
#> $...
#> 
#> 
#> $na.rm
#> [1] FALSE
#> 
#> $show.legend
#> [1] NA
#> 
#> $inherit.aes
#> [1] TRUE

^{Created on 2020-02-25 by the reprex package (v0.3.0)}

test <- function(
  x = 1,
  y = 2,
  ...
) {
  if(length(list(...)) == 0) {
    print(as.list(environment()))
  } else {
    print(c(as.list(environment()), list(...)))
  }
}

test()
test(z = 3)