How can I remove all objects but one from the workspace in R?

I have a workspace with lots of objects and I would like to remove all but one. Ideally I would like to avoid having to type rm(obj.1, obj.2... obj.n). Is it possible to indicate remove all objects but these ones?

Here is a simple construct that will do it, by using setdiff:

rm(list=setdiff(ls(), "x"))

And a full example. Run this at your own risk - it will remove all variables except x:

x <- 1
y <- 2
z <- 3
ls()
[1] "x" "y" "z"

rm(list=setdiff(ls(), "x"))

ls()
[1] "x"

Using the keep function from the gdata package is quite convenient.

> ls()
[1] "a" "b" "c"

library(gdata)
> keep(a) #shows you which variables will be removed
[1] "b" "c"
> keep(a, sure = TRUE) # setting sure to TRUE removes variables b and c
> ls()
[1] "a"