[R] adding mean to boxplot

[Johannes Ullrich]

I am a new and unexperienced user of R and got so far as to know how to produce 
boxplots. I have no experience of messing with function code, so presently I do 
not know how to create a boxplot with group means instead of group medians. If 
somebody could help me either replace the median with the mean or superimpose 
the mean onto the existing boxplot, it would be appreciated.