[R] Alternate tick labels in xyplot

[Lisa Daniel]

Dear Rhelp,

I would like to get alternate tick labels for the xyplot:
library(lattice)
library(grid)

xy <-xyplot(decrease ~ treatment, OrchardSprays,
    main= "Some plot",
        groups = rowpos, type = "a",
                page     = function(n){
                         grid.text(LETTERS[j],
                         y = 0.95,
                         x = 0.15,
                         default.units = "npc",
                         just = c("left"),
                         gp = gpar(fontsize = 12,fontface="bold") )
                       },
    par.settings = c(simpleTheme(lty=1:8, col="black",lwd=2),list(layout.heights = list(main = 1.2,
                       sub  = 0,
                       axis.top = 0.2,
                       top.padding  = 0.1,
                       bottom.padding = 0)) ),
        auto.key = list(x = 0.2, y = 0.9,
        cex = 0.75, points = FALSE, lines = TRUE)) 
j=1
print(xy, pos = c(0.0, 0.5, 0.33, 1.0), more = TRUE)
j=j+1
print(xy, pos = c(0.33, 0.5, 0.66, 1.0), more = TRUE)
j=j+1
print(xy, pos = c(0.66, 0.5, 0.99, 1.0), more = TRUE)
j=j+1
print(xy, pos = c(0.0, 0.0, 0.33, 0.5), more = TRUE)
j=j+1
print(xy, pos = c(0.33, 0.0, 0.66, 0.5), more = TRUE)
j=j+1
print(xy, pos = c(0.66, 0.0, 0.99, 0.5), more = FALSE)


similar to the x-axis in the code below, but somehow it is not working when I pasted 'list(axis.components=...) in the above code:
xyplot(rnorm(12) ~ 1:12 , type="l",
scales=list(x=list(at=seq(2,12,2),labels=c(1, ' ', 3 , ' ' , 5 , ' ' ))),
par.settings=list(axis.components=list(bottom=list(tck=c(0,1))))) 

scales=list(x=list(at=seq(1,8,1),labels=c('A', ' ', 'C', ' ' ,'E' , ' ','G',' '))),

If possible, I would like a heading for each rows (justified to center) above the individual heading.

Please help.
Many thanks,
Lisa.