[R] Jitter in xYplot?

[John Poulsen]

Hello,

The simple example below plots three species by year and site.  However, 
  I would like the points to occur in groups horizontally, rather than 
on top of each other.

I thought jitter might work, but haven't been successful in getting it 
to do what I want.

Any ideas?  Thanks in advance.

John



wt=rnorm(27,5,0.6)
yr=rep(c(2000,2001,2002),each=3)
vill=c("Kabo","Pkl","Lnd")
spp=c("A","B","C")
df=data.frame(wt,yr,vill,spp)
err=wt*0.025

xYplot(Cbind(wt, wt-err, wt+err)~yr|factor(vill), groups=factor(spp), 
    	data=df,scales=list(alternating=1, y=list(relation="free"), 		 
x=list(at=c(2000,2001,2002))))