[R] Binning question (binning rows of a data.frame according toa variable)

[Alexander Nervedi]

I dont as yet fully understand how trellis works. Advice would be much 
appreciated.

I have a factor variable (2 levels) and a continuous variable and I am able 
to plot a histogram of the frequencies of the continuous variable for each 
level of the factor variable using :


histogram( ~ class | one, data = data,
                                    xlab = "Grades", type = "density",
                                             panel = function(x, ...) {
                                              panel.histogram(x, ...)
                                  
panel.mathdensity(dmathjavascript:G('/cgi-bin/hmhome?');
Today = dnorm, col = "black",
                                        args = list(mean=mean(x),sd=sd(x)))
The two distributions overlap over an area and I would like to draw vertical 
lines to demark the lower tail of the distribution which has a higher 
median, and the right tail of the distribution with lower  median.

Any suggestion would be really helpful.
thanks

ul-nadi