title: How to shade a region under a curve using ggplot2
body: <p>I've been trying to use ggplot2 to produce a plot similar to this R graphic:</p>
  
  <pre><code>xv&lt;-seq(0,4,0.01)
  yv&lt;-dnorm(xv,2,0.5) 
  plot(xv,yv,type="l") 
  polygon(c(xv[xv&lt;=1.5],1.5),c(yv[xv&lt;=1.5],yv[xv==0]),col="grey") 
  </code></pre>
  
  <p>This is as far as I've gotten with ggplot2:</p>
  
  <pre><code>x&lt;-seq(0.0,0.1699,0.0001)   
  ytop&lt;-dnorm(0.12,0.08,0.02)
  MyDF&lt;-data.frame(x=x,y=dnorm(x,0.08,0.02))
  p&lt;-qplot(x=MyDF$x,y=MyDF$y,geom="line") 
  p+geom_segment(aes(x=0.12,y=0,xend=0.12,yend=ytop))
  </code></pre>
  
  <p>I would like to shade the tail region beyond x=0.12. How would I do this using ggplot or qplot? </p>
  
  <p>Broadly, how does one shade any subset under the curve, whether a tail, or between two arbitrary lines dividing the region into distinct areas?</p>
  
  <p>Thanks for any advice.</p>