r vector that specifies the grouping
variable(s). Padding will take place within the different groups. When
interval is not specified, it will be determined applying <code>get_interval</code>
on the datetime variable as a whole, ignoring groups (see last example).</p></td>
    </tr>
    <tr>
      <th>break_above</th>
      <td><p>Numeric value that indicates the number of rows in millions
above which the function will break. Safety net for situations where the
interval is different than expected and paddin