Draw grid lines on specific values in xyplot

Question

I have a xyplot and I want to draw grid lines on the 0 values.

How this can be done?

Answer 1

There is a lattice llines function that replaces the function of lines() functionality in base. There is also a panel.lines function.

#---------- method --------------
 xyplot(-1:1 ~ -1:1, type="l")
trellis.focus("panel", 1, 1)
do.call("panel.abline", list(h=0,v=0, lty=3) )
trellis.unfocus()
# --- that method has the advantage of also demonstrating 
#        how to modify an existing plot

#---------- method 2--------------

 xp <-xyplot(-2:1 ~ -2:1, type="l", panel=function(...){
 panel.xyplot(...)
 panel.abline(h=0,v=0, lty=3)} )
xp