How to custom the tick and type in bwplot

Dear R users

I use bwplot to plot some figures.  There are two troubles:

1. How to change the dot of the mean to a line, like the style in  
boxplot

2. How to hide some tick marks.  For example, I have seven tick: A,  
B, C, D,
E, F, G,
   but I want show four marks: A, C, E, G on the x-axis.

 On Apr 24, 2009, at 1:33 PM, Guanghong Zuo wrote:

Dear R users

I use bwplot to plot some figures.  There are two troubles:

1. How to change the dot of the mean to a line, like the style in boxplot

 Sometimes you need to refer the the help page for panel.<type of plot>, in
this case:
 ?panel.bwplot

 ... so the answer is now staring you in the face:
 bwplot(decrease ~ treatment, OrchardSprays, groups = rowpos, pch="|")

2. How to hide some tick marks.  For example, I have seven tick: A, B, C,

D,

E, F, G,
  but I want show four marks: A, C, E, G on the x-axis.

 Using the example in bwplot again, and a fair amount of fruitless
experimentation with the theory that one could do anything useful with
scales=list(at= list(<something>)), I finally ended up trying , labels=c( )
per Sarkar's Lattice book, producing this:

 bwplot(decrease ~ treatment, OrchardSprays, groups = rowpos,
scales=list(x=list( labels=c("A","","","D","","F","","")
)))