title: Eliminating all data over a given percentile
body: <p>I have a pandas <code>DataFrame</code> called <code>data</code> with a column called <code>ms</code>.  I want to eliminate all the rows where <code>data.ms</code> is above the 95% percentile.  For now, I'm doing this:</p>
  
  <pre><code>limit = data.ms.describe(90)['95%']
  valid_data = data[data['ms'] &lt; limit]
  </code></pre>
  
  <p>which works, but I want to generalize that to any percentile.  What's the best way to do that?</p>