kartik\grid\ColumnTrait::calculateSummary PHP Method

    protected function calculateSummary()
    {
        $data = $this->_rows;
        $type = $this->pageSummaryFunc;
        if ($type instanceof Closure) {
            return call_user_func($type, $data);
        }
        if (empty($this->_rows)) {
            return '';
        }
        switch ($type) {
            case null:
                return array_sum($data);
            case GridView::F_SUM:
                return array_sum($data);
            case GridView::F_COUNT:
                return count($data);
            case GridView::F_AVG:
                return count($data) > 0 ? array_sum($data) / count($data) : null;
            case GridView::F_MAX:
                return max($data);
            case GridView::F_MIN:
                return min($data);
        }
        return '';
    }