[R] group by-like statement for 2-row matrix

[Hans-Henning Gabriel]

Hi,

my problem is as follows:

I have a matrix of two rows like this:

2 2 3 4 4 4 5 5 6
1 1 2 1 3 3 2 1 1

Can I apply something like "group by" in sql? What I want to achieve  
is the some of second row for each unique entry of first row:

2 -> 2 (=1+1)
3 -> 2
4 -> 7 (=1+3+3)
5 -> 3 (=2+1)
6 -> 1

Thanks!!
Henning