[R] sum(row1==y) if row2=x

[Knut Krueger]

Hi to all
is there any construct to sum
data=data.frame(row1=c(1,1,3,1,2,3,2,2,1,3,4,5,2,3,2,1) ,
                          row2=c(2,2,1,1,1,2,1,2,1,1,1,1,2,2,2,1) )
Means I would like to get all y of row1 if in row2 of the data.frame is 
an x
f.e row1=3 and row2=2
so I would like to get 6

And is there another construct to get the count of pairs where
row1=3 and row2=2
means the result should be 2
I could do this with loop but I am wondering whether there is any better 
way.

Regards Knut