Functions with a number of "dynamic" arguments

Question

want to construct a function that can have the number of variable parameters, as the function c, and how to access their addresses, for example:

c(a = 1, b = 2, d = 9)
#acessar a, b e d

Has something to do with ...? What do they mean?

Answer 1

dot-dot-dot or ... is called ellipse.

minha_funcao_com_elipse <- function(...) {
  input_list <- list(...)
  input_list
}

See the result of this function:

> minha_funcao_com_elipse(a = 1, b= 2, c= 3)
$a
[1] 1

$b
[1] 2

$c
[1] 3

Note that the command input_list <- list(...) creates a list of all parameters that have been passed within the ellipse.

Like input_list is a common list of R, it is easy to access its elements. The function c, for example could be imitated as follows:

> c2 <- function(...) {
+   unlist(list(...))
+ }
> c2(a = 1, b= 2, c= 3, 5, 6)
a b c     
1 2 3 5 6 

Is it worth reading this response from the OS. Another good reference is the Advanced R in the session ....

Answer 2

You can define a function using the ..., which can be used to access arguments explicitly passed by name. To access the values, you convert the ... in a list (using list(...)). The code below shows an example:

c <- function(...) {
    args <- list(...)
    argNames <- names(args)
    print(argNames)
    sum(sapply(args, function(x) x))
}

c(a = 1, b = 4, d = 9)