how to merge row in asp.net?

Question

 for (int rowIndex = gridView.Rows.Count - 2; rowIndex >= 0; rowIndex--)

        {

            GridViewRow row = gridView.Rows[rowIndex];

            GridViewRow previousRow = gridView.Rows[rowIndex + 1];

            for (int i = 0; i < row.Cells.Count; i++)

            //for (int i = 0; i < cnt; i++)

            {

                string rowcell = row.Cells[i].Text;

                string previousRowCell = previousRow.Cells[i].Text;

                if (row.Cells[i].Text == previousRow.Cells[i].Text  && i==11)

                {

                   // int j = i + 1;

                    row.Cells[i].RowSpan = previousRow.Cells[i].RowSpan < 2 ? 2 : previousRow.Cells[i].RowSpan + 1;

                    previousRow.Cells[i].Visible = false;

                }

            }

        }