title: Order dataframe chronologically based on dates which are formatted %d/%m/%Y
body: <p>I have some data that has to be formatted as (%d/%m/%Y). The data is out of chronological order because it is sorted by the first number which is the day, not the month.  </p>
  
  <p>I'm hoping I can specify to <code>order</code> or <code>reorder</code> that I want the sorting to happen differently.  I'm just not sure how to do this.  </p>
  
  <p>Here is some date data to be ordered:</p>
  
  <pre><code>date
  1/1/2009  
  1/1/2010
  1/1/2011
  5/4/2009
  5/4/2011
  10/2/2009
  10/3/2011
  15/9/2010
  15/3/2009
  31/12/2011
  31/7/2009
  </code></pre>
  
  <p>Thanks for any suggestions.</p>