title: Date Conversion mm/dd/yyy hh:mm:ss to yyyy-mm-dd in R
body: <p>I would like to convert the data frame</p>
  
  <p><code>12/31/2012 23:49:18<br>
   12/30/2012 20:27:17<br>
  12/29/2012 20:21:24
  </code>  </p>
  
  <p>to </p>
  
  <p><code>2012-12-31<br>
   2013-12-30<br>
   2013-12-29</code>  </p>