title: How to plot two charts with same X axis in R?
body: <p>How do I plot 2 charts using the same x axis in R with ggplot2?</p>
  
  <p>I am looking for something like:
  <a href="http://i.stack.imgur.com/B9QT7.png" rel="nofollow">http://i.stack.imgur.com/B9QT7.png</a></p>