Question

Suppose I have a function

test <- function(s,t) {
..
}
that requires two arguments.

How can I make it so that it also takes one single argument, i.e. test(t) would return test(t,t)? Thanks in advance.

Answer 1

Because R uses lazy evaluation you can set the default value of the second argument equal to the first argument …

foo <- function(s,t=s) {
   s+t
 }
> foo(4)
[1] 8
> foo(4,5)
[1] 9