perfectionism

I have a named vector:

z<- c(1, 2, 3, 2)
names(z)<- c("a","b","c","b")
f<- c("b","c")

I want to know the index in z of the first occurrence of each of the values in f.

One implementation is

sapply(f, function(x) which(names(z)==x)[1])

b c
2 3

Is which() smart enough to stop when it finds in z the first occurrence of every
value from f, or does it search through all the values in z only to report the
first one?

Are some more elegant ways of writing this code?

Just curious.