stem.R

#function adapted from http://mpastell.com/2009/09/11/matlab-style-stem-plot-with-r/
stem = function(x,y,slope,intercept,pch=16,linecol=2,clinecol=1,lty=2,from_mean=FALSE,...){
    if (missing(y)){
        y = x
        x = 1:length(x) 
    }
    
    #this plots the points
    plot(x,y,pch=pch,...)
    
    #this plots the line
    abline(intercept,slope)
    
    if (from_mean) {
        #plot the mean line
        abline(mean(y),0,lty=1,col=1)
        
        #this plots the stem lines to the mean line
        for (i in 1:length(x)){
           lines(c(x[i],x[i]), c(mean(y),slope*x[i]+intercept),col=linecol,lty=lty)
        }
    }
    else {
        #this plots the stem lines to each point
        for (i in 1:length(x)){
           lines(c(x[i],x[i]), c(y[i],slope*x[i]+intercept),col=linecol,lty=lty)
        }
    }

}