protected function _group($group, $args, $options)
{
$conditions = $args['conditions'];
$group += array('$reduce' => $args['reduce'], 'initial' => $args['initial']);
$command = array('group' => $group + array('ns' => $args['source'], 'cond' => $conditions));
$stats = $this->connection->command($command);
$data = isset($stats['retval']) ? $stats['retval'] : null;
unset($stats['retval']);
return compact('data', 'stats');
}