如何把合并行的这段代码改成合并列的
  public static void GroupRows(GridView GridView1, int cellNum)
        {
            int i = 0, rowSpanNum = 1;
            while (i < GridView1.Rows.Count - 1)
            {
                GridViewRow gvr = GridView1.Rows[i];
                for (++i; i < GridView1.Rows.Count; i++)
                {
                    GridViewRow gvrNext = GridView1.Rows[i];
                    if (gvr.Cells[cellNum].Text == gvrNext.Cells[cellNum].Text)
                    {
                        gvrNext.Cells[cellNum].Visible = false;
                        rowSpanNum++;
                    }
                    else
                    {
                        gvr.Cells[cellNum].RowSpan = rowSpanNum;
                        rowSpanNum = 1;
                        break;
                    }

                    if (i == GridView1.Rows.Count - 1)
                    {
                        gvr.Cells[cellNum].RowSpan = rowSpanNum;
                    }
                }
            }
        }