R help - Nov 2008 - How to detect NULL list element?

I have a list that starts out like:

r <- list()
r[[3]] <- list(count=1, orderlist=data.frame(count=1, sku="A"))

So r[3] yeilds:

[[1]]
[[1]]$count
[1] 1

[[1]]$orderlist
  count sku
1     1   A

So far so good. Now I want to detect the fact that there is no etry in 1,2, and
4.
> r[1]
[[1]]
NULL
> is.null(r[1])
[1] FALSE

So how do I detect the NULL at r[1]?

Thank you.

Kevin

2008/11/3  <rkevinburton at charter.net>:
> So how do I detect the NULL at r[1]?
 How can you detect what is not there?

 Single square brackets on a list give you a list. Double square
brackets give you the elements.

 is.null(r[[1]]) should be TRUE.

Barry