function hook_aggregation_info() {
  $new_aggregation_methods = array(
    'group_concat' => array(
      'title' => t('Group Concat'),
      'method' => 'views_query_default_aggregation_method_simple',
      /* This uses the default aggregate callback, which simply uppercases the array index for this function and wraps it around the field with parenthesis*/
      'handler' => array(
        'argument' => 'views_handler_argument_group_by_numeric',
        'filter' => 'views_handler_filter_group_by_numeric',
        'sort' => 'views_handler_sort_group_by_numeric',
      ),
    ),
    'sum_positive' => array(
      'title' => t('Sum Positive Values'),
      'method' => 'views_query_sum_polar_aggregation', // Custom function below.
      'handler' => array(
        'argument' => 'views_handler_argument_group_by_numeric',
        'filter' => 'views_handler_filter_group_by_numeric',
        'sort' => 'views_handler_sort_group_by_numeric',
      ),
    ),
    'sum_negative' => array(
      'title' => t('Sum Negative Values'),
      'method' => 'views_query_sum_polar_aggregation', // Custom function below.
      'handler' => array(
        'argument' => 'views_handler_argument_group_by_numeric',
        'filter' => 'views_handler_filter_group_by_numeric',
        'sort' => 'views_handler_sort_group_by_numeric',
      ),
    ),
    'coalesce' => array(
      'title' => t('Coalesce'),
      'method' => 'views_query_default_aggregation_method_simple',
      'handler' => array(
        'argument' => 'views_handler_argument_group_by_numeric',
        'filter' => 'views_handler_filter_group_by_numeric',
        'sort' => 'views_handler_sort_group_by_numeric',
      ),
    ),
  );
  return $new_aggregation_methods;
}

function views_query_sum_polar_aggregation($group_type, $field) {
  $condition = ($group_type == 'sum_positive') ? '>' : '<';
  return 'SUM(IF(' . $field . $condition . '0, ' . $field . ', 0))';
}