title: slick one-lineRs
body: <p>What's your favorite one-liner in <code>R</code>? </p>
  
  <p>Include a short companion example, and limit to one tip per post, please.
  Note, <code>;</code> is cheating. </p>
  
  <p>Example: calculate <code>x[i] / x[i-1]</code> for a vector <code>x</code>,</p>
  
  <pre><code>x &lt;- 1:10
  Reduce("/", as.data.frame(embed(x, 2)))
  </code></pre>
  
  <p>(collected from R-help, I forget who/when)</p>
  
  <p><em>Edit:</em> after some initial controversy, it looks like the question is now reopen for entries.</p>