[R] Optional variables in function?

[Jonathan Greenberg]

I'm a bit new to writing R functions and I was wondering what the "best
practice" for having optional variables in a function is, and how to test
for optional and non-optional variables?  e.g. if I have the following
function:

helpme <- function(a,b,c) {


}

In this example, I want c to be an optional variable, but a and b to be
required.  How do I:
1) test to see if the user has inputted c
2) break out of the function of the user has NOT inputted a or b.

Thanks!

--j

--

Jonathan A. Greenberg, PhD
NRC Research Associate
NASA Ames Research Center
MS 242-4
Moffett Field, CA 94035-1000
Phone: 415-794-5043
AIM: jgrn3007
MSN: jgrn3007 at hotmail.com