title: format a Date column in a Data Frame
body: <p>I've the following data from a data frame</p>
  
  <pre><code>Name,JoiningDate,AmtPaid
  Joe,12/31/09,1000
  Amy,10/28/09,100
  John,05/06/10,200
  </code></pre>
  
  <p>The Joining Date is coming in as a factor (when I <code>sapply</code>). How can I convert this to date and then sort on <code>JoiningDate</code>?</p>