How to know the arguments contained in '...' in a function in R?

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In R can be used '...' so that the function receives an undetermined number of arguments.

How to know which arguments were used in the function?

Example, if I wanted to print the arguments used.

imprimeArgumentos <- function(...) {
  args <- #pega os argumentos contidos em ´...´
  print(args)
}

The function shall function as follows:.

imprimeArgumentos(x=3, z=NULL, y=3) 

$x
[1] 3

$z
NULL

$y
[1] 3
r

1 answer

6


A simple way to capture the arguments is to put them in a list:

imprimeArgumentos <- function(...) {
  args <- list(...)
  print(args)
}

imprimeArgumentos(x=3, z=NULL, y=3) 
#> $x
#> [1] 3
#> 
#> $z
#> NULL
#> 
#> $y
#> [1] 3

If you want to work with Lazy Evaluation, you can use substitute and only make the Valuation of arguments when timely:

imprimeArgumentos <- function(...) {
   # vai te retornar uma expressão da lista e não a lista em si
  args <- substitute(list(...))
  print(args)
}
imprimeArgumentos(x=3, z, y=3)
#> list(x = 3, z, y = 3)

Note that in this last example, z does not exist, but function gives no error as we have not yet evaluated the content of the list.

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