keep the row indexes/names when do aggregate

Hi, R-users,

If I have a data frame like this:

x<-data.frame(g=c("g1","g2","g1","g1","g2"),v=c(1,7,3,2,8))

  g v
1 g1 1
2 g2 7
3 g1 3
4 g1 2
5 g2 8


It contains two groups, g1 and g2. Now for each group I want the max v:

aggregate(x$v,list(g=x$g),max)

  g x
1 g1 3
2 g2 8

Beautiful. But what if I want to keep the row index of (g1 3) and (g2 8) in the original x?
So I want is:

do something

  g x
 3 g1 3
 5 g2 8

Of course it'd may make much more sense if the row indexes are some row names that I want to keep.

Is there a simple way to do that?

Thanks a lot!

Z