plyr and table question

That makes sense, so I can do something like,

count <- function(x){
? ? ? ?as.integer(unclass(table(x)))
}

count(d$user_id)

ddply(d, .(user_id), transform, count = count(user_id))

?user_id ?website time count
1 ? ? ?20 ? google ?930 ? ? 2
2 ? ? ?20 facebook 1000 ? ? 2
3 ? ? ?21 ? ?yahoo ?935 ? ? 1
4 ? ? ?25 facebook 1015 ? ? 1
5 ? ? ?61 ? google ?940 ? ? 1

Have I missed a built-in function to obtain this result?