indicates the index of the column in <code>x</code> that stores the date and times <br>
If <code>dates</code> is a factor, it is converted into POSIXct class, using the date format specified by <code>date.fmt</code>  <br>
If <code>dates</code> is already of POSIXct or POSIXt class, the code verifies that the number of elements on it be equal to the number of elements in <code>x</code></p></dd>

  <dt>date.fmt</dt>
<dd><p>character indicating the format in which the dates are stored in <code>dates</code>, By