[R] representing NULL values in a vector

[Duncan Murdoch]

On 06/09/2010 1:00 AM, rajeshj at cse.iitm.ac.in wrote:
> Hi,
> 
> I have a vector who contents should look like this,
> 
> "c" "d" NULL "e" "f" etc
> or 
> 4 5 6 NULL 7 8 9
> 
> how can I represent the null value?

As others have said, you probably want NA rather than NULL.  If you 
really want NULL, then use a list (a generic vector).  So

x <- list("c", "d", NULL, "e", "f")
y <- list(4,5,6,NULL, 7,8,9)

You need to be careful when setting values, because

y[[1]] <- NULL

will *remove* element 1, not set it to NULL.  To set it to NULL, use

y[1] <- list(NULL)

Duncan Murdoch