R: using a list for ellipsis arguments

Question

I have run into a situation where I need to take all the extra arguments passed to an R function and roll them into an object for later use. I thought the previous question about ellipses in functions would help me, but I still can't quite grasp how to do this. Here is a very simple example of what I would like to do:

newmean <- function(X, ...){
  args <- as.list(substitute(list(...)))[-1L]
  return(mean(X, args))
}

I've tried a number of different formulations of args in the above example and tried unlisting args in the return call. But I can't make this work. Any tips?

I realize that I could do this:

newmean <- function(X, ...){
    return(mean(X, ...))
}

But I need to have the ... arguments in an object which I can serialize and read back into another machine.

Answer 1

How about

newmean <- function(X, ...){
  args <- as.list(substitute(list(...)))[-1L]
  z<-list(X)
  z<-c(z,args)
  do.call(mean,z)
}

Answer 2

Can I ask what's the difference between args <- list(...) and args <- as.list(substitute(list(...)))[-1L]? And what's the do.call magic here?

since for this question, code below works too

newmean <- function(X, ...){ args <- list(...); do.call(mean,c(list(X),args)) }

But this does not work: newmean <- function(X, ...){ args <- list(...); mean(c(list(X),args)) } `