R check if any missing arguments

Question

I have a function with MANY arguments. I need to throw an error if ANY of them are missing:

This can be done like so:

testFunction = function(a,b,c,d,e,f,g,....){
  if(missing(a)) stop("a is required")
  if(missing(b)) stop("b is required")
  if(missing(c)) stop("c is required")
  if(missing(d)) stop("d is required")
  if(missing(e)) stop("e is required")
  if(missing(f)) stop("f is required")
  if(missing(g)) stop("g is required")
}

But my actual case contains many more arguments than the above trivial example, and as such, I would rather execute an equivalent check using a loop, something like this: (which doesn't work)

testFunction = function(a,b,c,d,e,f,g,...){
  args = as.list(environment())
  for(n in names(args)){
    if(missing(as.name(n))) stop(sprintf("%s is required",n))
  }
}

The above throws an error:

Error in missing(as.name(n)) : invalid use of 'missing'

How can I check whether an argument is missing by a character representation of the argument name?

Answer 1

What about something like this instead

f <- function(a,b,c,d) {
    defined <- ls()
    passed <- names(as.list(match.call())[-1])

    if (any(!defined %in% passed)) {
        stop(paste("missing values for", paste(setdiff(defined, passed), collapse=", ")))
    }
    a+b+c+d
}

And it works like this

f(1)
# Error in f(1) : missing values for b, c, d
f(2, d=3)
# Error in f(2, d = 3) : missing values for b, c
f(1,2,3,4)
# [1] 10

Basically we use ls() to get a list of variables in the function at the time (which should be all the arguments) and then we use match.call() to see what was actually passed to the function.