[R] lattice ltext

[Troels Ring]

Dear friends - please give me a hand.
I have a dataset of 40 patients in two groups observed on three 
occasions. I only want to plot a line
for each patient in the two groups. I use the ltext  function to put the 
patient  number but fail to make lattice understand the numbers as 
unique since apparently it starts all over with 1:20 for each panel 
instead of respecting my desires to have 1:20 and then 21:40.
I'm on windows vista, R2.9.2
Best wishes
Troels

score <-  runif(120,0,100)
pt <- gl(40,3,120)
times <- rep(c(0,3,6),40)
trt <- gl(2,60,120)
ach <- data.frame(score=score,pt=pt,times=times,trt=trt)

myPanel <- function(x,y,...){
panel.xyplot(x,y,...)
ltext(x-.1,y+1,paste(pt),cex=0.5) }

xyplot(score~times|trt,groups=pt,type=c("p","l"),ach,
panel=myPanel)

-- 
Troels Ring
Department of nephrology
Aalborg Hospital
Mølleparkvej 
phone: +4599326629

Heliosvej 12
9210 Aalborg SØ
98140582
30480176