shadenorm2.R

# by Tony Cookson
# http://www.r-bloggers.com/how-to-shade-under-a-normal-density-in-r/

shadenorm = function(below=NULL, above=NULL, pcts = c(0.025,0.975), mu=0, 
	sig=1, numpts = 500, color = "gray", dens = 40, justabove= FALSE, 
	justbelow = FALSE, lines=FALSE, between=NULL, outside=NULL, plotwidth=NULL) {
                     
    if(is.null(between)){
         below = ifelse(is.null(below), qnorm(pcts[1],mu,sig), below)
         above = ifelse(is.null(above), qnorm(pcts[2],mu,sig), above)
    }
   
    if(is.null(outside)==FALSE){
         below = min(outside)
         above = max(outside)
    }
    lowlim = mu - plotwidth*sig
    uplim  = mu + plotwidth*sig
           
    x.grid = seq(lowlim,uplim, length= numpts)
    dens.all = dnorm(x.grid,mean=mu, sd = sig)
    if(lines==FALSE){
          plot(x.grid, dens.all, type="l", xlab="X", ylab="Density")
    }
    if(lines==TRUE){
          lines(x.grid,dens.all)
    }
   
    if(justabove==FALSE){
        x.below    = x.grid[x.grid<below]
        dens.below = dens.all[x.grid<below]
        polygon(c(x.below,rev(x.below)),c(rep(0,length(x.below)),rev(dens.below)),col=color,density=dens)
    }
    if(justbelow==FALSE){
        x.above    = x.grid[x.grid>above]
        dens.above = dens.all[x.grid>above]
        polygon(c(x.above,rev(x.above)),c(rep(0,length(x.above)),rev(dens.above)),col=color,density=dens)
    }
   
    if(is.null(between)==FALSE){
         from = min(between)
         to   = max(between)
         
         x.between    = x.grid[x.grid>from&x.grid<to]
         dens.between = dens.all[x.grid>from&x.grid<to]
         polygon(c(x.between,rev(x.between)),c(rep(0,length(x.between)),rev(dens.between)),col=color,density=dens)
    }
   
}