title: Tornado Chart/Diagram with ggplot2
body: <p>I'm having a spot of difficulty getting <a href="http://en.wikipedia.org/wiki/Tornado_diagram" rel="nofollow">this</a> to output right... </p>
  
  <p>Here's what I've tried so far: </p>
  
  <p>sample data: </p>
  
  <pre><code>dat &lt;- data.frame(
  variable=c("A","B","A","B"),
  Level=c("Top-2","Top-2","Bottom-2","Bottom-2"),
  value=c(.2,.3,-.2,-.3)
  )
  </code></pre>
  
  <p>This is the closest I've got so far: </p>
  
  <pre><code>ggplot(dat, aes(variable, value, fill=Level)) + geom_bar(position="dodge")
  ## plots offset, as expected
  ggplot(dat, aes(variable, value, fill=Level)) + geom_bar(position="stack") 
  # or geom_bar(), default is stack but it overplots
  </code></pre>