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.

I completely misunderstood your question so I delete my answer. One thing to add - use `substitute[-1L]` hack only when is needed, if you need values only then `list(...)` is sufficient, if you want pass arguments further then pass as `...`. — Marek, Jun 30 '10 at 06:53

score 12 · Accepted Answer · answered Jun 29 '10 at 16:57

12

How about

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

answered Jun 29 '10 at 16:57

Jyotirmoy Bhattacharya

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you've been helping me a lot lately! Thanks again. – JD Long Jun 29 '10 at 18:55
@JD, am learning stuff too in trying to answer your questions. – Jyotirmoy Bhattacharya Jun 30 '10 at 01:36
2

Why the trouble? A simple `list(...)` seems to solve the problem. – qed Mar 10 '15 at 13:16
@qed That example comes from data.frame. No one seems to be able to figure out what edge case it was trying to avoid. – Brandon Bertelsen Oct 20 '16 at 03:00

R: using a list for ellipsis arguments

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