R: check mandatory/required arguments are provided - r

Question

I'd like to be able to have a way to check all arguments without defaults are specified when calling a function in R. This seems like a sensible thing to do to me, as it avoids a function failing later on (which could be after a lot of processing) when a value is found to be missing.
One way to accomplish this task would be to write a if (missing(arg)) statement for each argument, but this requires keeping the arguments for the function and the above statements consistent with each other, so I'm looking for a better solution.
At present I use the following function, which works in most cases, but not all.
# check for required arguments by getting arguments for the
# definition of the calling function and comparing to the arguments
# in the function call
check_required_args <- function () {
def <- sys.function(-1)
f_args <- formals(def)
f_args <- f_args[sapply(f_args, is.name)] # remove arguments with defaults
f_args <- names(f_args)
f_args <- f_args[f_args != '...'] # remove ellipsis argument if present
call <- match.call(definition=def, call=sys.call(-1))
f_name <- call[1]
c_args <- names(as.list(call[-1]))
for(n in f_args) {
if (!n %in% c_args) {
stop("Argument '", n, "' missing from call to function ",
f_name, "()", call.=FALSE)
}
}
}
f <- function(a, b, c=2) check_required_args()
f(a=1) # should fail (missing argument b)
f(2, 3) # should work
f(2, c=5) # should fail (missing argument b)
f(2, 3, 4) # should work
f <- function(a, b, ...) f2(a, b, ...)
f2 <- function(a, b, c, ...) check_required_args()
f2(a=1, b=2, c=3) # should work
f2(a=1, b=2) # should fail (missing argument c for function f2)
f(a=1, b=2, c=3) # should work
f(a=1, b=2) # should fail (missing argument c for function f2)
Can this function be improved to work in all of these cases? If not is there a more appropriate solution to perform this check?

Answer 1

Maybe this?
check_required_args <- function (fun = sys.function(-1), ncall = 3) {
f_args <- formals(fun)
f_args <- f_args[vapply(f_args, is.symbol, FUN.VALUE = TRUE)]
f_args <- names(f_args)
f_args <- setdiff(f_args, "...")
test <- vapply(f_args,
function(x) missingArg(as.name(x), envir = parent.frame(ncall), eval = TRUE),
FUN.VALUE = TRUE)
stopifnot(!any(test))
return(invisible(NULL))
}
f <- function(a, b, c=2) {
check_required_args()
return("Hello!")
}
f(a=1) # should fail (missing argument b)
#Error: !any(test) is not TRUE
f(2, 3) # should work
#[1] "Hello!"
f(2, c=5) # should fail (missing argument b)
# Error: !any(test) is not TRUE
f(2, 3, 4) # should work
#[1] "Hello!"
x <- 1
f(a=x, 3)
#[1] "Hello!"
f <- function(a, b, ...) f2(a, b, ...)
f2 <- function(a, b, c, ...) {
check_required_args()
return("Hello!")
}
f2(a=1, b=2, c=3) # should work
#[1] "Hello!"
f2(a=1, b=2) # should fail (missing argument c for function f2)
#Error: !any(test) is not TRUE
f(a=1, b=2, c=3) # should work
#[1] "Hello!"
f(a=1, b=2) # should fail (missing argument c for function f2)
#Error: !any(test) is not TRUE
Edit:
You might want to use get to check for existence:
check_required_args <- function (fun = sys.function(-1), ncall = 3) {
f_args <- formals(fun)
f_args <- f_args[vapply(f_args, is.symbol, FUN.VALUE=TRUE)]
f_args <- names(f_args)
f_args <- setdiff(f_args, "...")
test <- lapply(f_args,
function(x) {
get(x, envir = parent.frame(ncall), inherits = TRUE)
return(NULL)
})
#possibly use a for loop instead
#wrap in tryCatch for customized error messages
}
f <- function(a, b, ...) f2(a, b, ...)
f2 <- function(a, b, c, ...) {
check_required_args()
return("Hello!")
}
f(c=2)
#Error in get(x, envir = parent.frame(ncall), inherits = TRUE) :
# argument "a" is missing, with no default
If you don't want check in enclosing frames, set inherits = FALSE.