title: Is it possible to split X-Axis labels into two levels?
body: <p>My X-axis labels are strings and rotating them is making my plot look ugly. In ggplot, is there a way to split up the X-axis labels such that half of them appear on the top and half on the bottom (alternating style). So instead of:</p>
  
  <pre><code>Label1 Label2 Label3 Label4
  </code></pre>
  
  <p>I want:</p>
  
  <pre><code>Label1   Label3
      Label2    Label4
  </code></pre>