CODEWITHSUNDEEP
rfunctionargumentsclosures
romants
romants

Reputation: 3648

Access evaluated function arguments R

How is it possible to access evaluated arguments to a function in case arguments have missing values.

Assuming the function is defined like.

foo <- function(...){
# function body
}

How to access arguments to function in its body, if some arguments are missing?

In case of no missing value, the answer is just

foo <- function(...){
  args <- list(...)
}

But this will not work if we do a call like foo(1,,3).

And other way I was able to find

foo <- function(...){
  args <- as.list(match.call())[-1]
}

Gives a list of arguments but they are not evaluated. For example for call foo(rnorm(10), 1, 2) args will contain unevaluated arguments, that I have sometimes troubling evaluating. Is there any meaningful way to do this?

UPD I need this because I want to write a wrapper functions that record arguments to function calls and return values. For example,

matrix_w <- function(...){
  args <- list(...)
  res <- matrix(...)
  return(res)
}

In a case of most calls it will work, but for call matrix_w(rnorm(20), , 2), it will not be able to process arguments in args <- list(...), but matrix(rnorm(20), , 2) works correctly.

Upvotes: 0

Views: 151

Answers (1)

MrFlick
MrFlick

Reputation: 206232

If you want them evaluated, you probably just should evaluate them yourself

matrix_w <- function(...){
  args <- as.list(match.call())[-1]
  eval.args <- lapply(args, function(x) tryCatch(eval(x), error=function(z) x))
  do.call(matrix, eval.args)
}

matrix_w(rnorm(10), , 2)

Upvotes: 1

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