The Number of Arguments to a Function

Description

When used inside a function body, nargs returns the number of arguments supplied to that function, including positional arguments left blank.

Usage

nargs()

Details

The count includes empty (missing) arguments, so that foo(x,,z) will be considered to have three arguments (see ‘Examples’). This can occur in rather indirect ways, so for example x[] might dispatch a call to `[.some_method`(x, ) which is considered to have two arguments.

This is a primitive function.

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

See Also

args, formals and sys.call.

Examples

tst <- function(a, b = 3, ...) {nargs()}
tst() # 0
tst(clicketyclack) # 1 (even non-existing)
tst(c1, a2, rr3) # 3

foo <- function(x, y, z, w) {
   cat("call was", deparse(match.call()), "\n")
   nargs()
}
foo()    # 0
foo(,,3) # 3
foo(z=3) # 1, even though this is the same call

nargs()# not really meaningful