[R] Plot subset of data per panel in Lattice xyplot

[modono]

Hello,
Apologies for the newbie question.
I have x,y data that I want to plot - I currently have a third column
which identifies the run.
 X, Y, RunNum

currenly I have xyplot(X,Y,data=xyplotdata, groups=RunNum) but there is
such alot of data -- what I want is another grouping that say would plot
xy data RunNum 1-9 in Panel1, RunNum 10-19 in Panel2 , RunNum 20-29 in
Panel3 etc,
Any help appreciated.  - I have tried variants of equal.count and
subsets - without success.
Thanks,