[R] Median abline how-to ?

[David martin]

Hi,
I'm newbie with R and don't really know how to add a median line to each 
of the groups that is not all the plot long.

Here is a small working code that i have adapted for my purpose. If 
somebody could tell me how to draw median lines on each group and not 
all plot long.

  ctl <- c(4.17,5.58,5.18,6.11,4.50,4.61,5.17,4.53,5.33,5.14)
      trt <- c(4.81,4.17,4.41,3.59,5.87,3.83,6.03,4.89,4.32,4.69)
      group <- gl(2,10,20, labels=c("Ctl","Trt"))
weight <- c(ctl, trt)

ctlmed <- median(weight[which(group == "Ctl")])
trtmed <- median(weight[which(group == "Trt")])
plot.default(weight ~ group,axes=F)
  axis(2,col.axis = "blue",las=1,cex.axis=0.7,xpd=TRUE)
  axis(1, 
labels=levels(group),at=1:length(unique(group)),las=2,cex.axis=0.7) 
#horizontal
abline(h = ctlmed, col = "blue", lwd = 2) # ?? how to make abline shorter ?
abline(h = trtmed, col = "red", lwd = 2)
box(bty="c")

ps: At this stage the boxplot is not interesting for me.
thanks,
david