Can I remove an element in ... (dot-dot-dot) and pass it on?

One way to manipulate these things is to wrap the child function inside parent, and use a definition that puts any arguments you don't want passing on to child after the ... argument. For example:

parent <- function(...) {    localChild <- function(..., toRemove) child(...)    localChild(...)}child <- function(a) {    a + 10}> parent(a = 1, toRemove = 10)[1] 11

Another way is to use do.call():

parent2 <- function(...) {    a <- list(...)    a$toRemove <- NULL    do.call(child2, a)}child2 <- function(b) {    b + 10}> parent2(b = 1, toRemove = 10)[1] 11

Depending on your actual use case, the do.call() is perhaps closest to what you intended with your Question.

Your child function is erroneous. Try

> child(a=1)Error in str(a) : object 'a' not found

edit : no longer applicable.

The ... argument should only be used to pass parameters to a next function. You cannot get the parameters from there that easily, unless you convert them to a list. So your child function could be :

child <- function(...){  mc <- match.call()  # or mc <- list(...)  str(mc$a)}

Which doesn't make sense. You can't know whether the user specified a or not. The correct way would be to include a as an argument in your function. the ... is to pass arguments to the next one :

child <- function(a, ...){    str(a,...)}

Then you could do :

parent <- function(...){   mc <- match.call()   mc$toRemove <- NULL   mc[[1L]] <- as.name("child")   eval(mc)}

or use the list(...) and do.call() construct @Gavin proposed. The benefit of match.call() is that you can include non-dot arguments as well. This allows your parent function to specify defaults for the child :

parent <- function(a=3, ...){    ... (see above)}