Split up `…` arguments and distribute to multiple functions

Question

Using the following function foo() as a simple example, I\'d like to distribute the values given in ... two different functions, if possible.

Answer 1

You can only pass the ... argument to another function, if that other function includes all named arguments that you pass to ... or if it has a ... argument itself. So for sum, this is no problem (args(sum) returns function (..., na.rm = FALSE)). On the other hand grep has neither na.rm nor ... as an argument.

args(grep)
# function (pattern, x, ignore.case = FALSE, perl = FALSE, value = FALSE, 
#     fixed = FALSE, useBytes = FALSE, invert = FALSE) 

This does not include ... and also does not include a named argument na.rm either. A simple solution is to just define your own function mygrep as follows:

mygrep <- function (pattern, x, ignore.case = FALSE, perl = FALSE, value = FALSE, 
                    fixed = FALSE, useBytes = FALSE, invert = FALSE, ...)
  grep(pattern, x, ignore.case, perl, value, fixed, useBytes, invert)

Then it seems to work:

foo <- function(x, y, ...){
  list(sum = sum(x, ...), grep = mygrep("abc", y, ...))
}
X <- c(1:5, NA, 6:10)
Y <- "xyzabcxyz"
foo(X, Y, na.rm = TRUE, value = TRUE)

# $sum
# [1] 56
# 
# $grep
# [1] "xyzabcxyz"