e, <code>.resolve = function(x) mean(x)</code> to get the mean value of all observations present for that individual/period. <code>.resolve</code> will also be used to fill in values if some values in a given individual/period are to be overwritten and others aren't. Using a function will be quicker than <code>.resolve = 'error'</code>, so if you're certain there's no issue, you can speed up execution by setting, say, <code>.resolve = dplyr::first</code>.</p></td>
    </tr>
    <tr>
      <th>.group_i</th>
