Test if an argument of a function is set or not in R
You use the function missing() for that.
f <- function(p1, p2) { if(missing(p2)) { p2=p1^2 } p1-p2}Alternatively, you can set the value of p2 to NULL by default. I sometimes prefer that solution, as it allows for passing arguments to nested functions.
f <- function(p1, p2=NULL) { if(is.null(p2)) { p2=p1^2 } p1-p2}f.wrapper <-function(p1,p2=NULL){ p1 <- 2*p1 f(p1,p2)}> f.wrapper(1)[1] -2> f.wrapper(1,3)[1] -1EDIT: you could do this technically with missing() as well, but then you would have to include a missing() statement in f.wrapper as well.
In a case like this you can also use something like this:
f <- function(p1, p2 = p1 ^ 2) { p1-p2}See the part on Lazy evaluation at http://adv-r.had.co.nz/Functions.html