protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
    {

        if (e.Row.RowType == DataControlRowType.DataRow)
        {
            //switch for first row
            if (e.Row.RowIndex == 1)
            {
                GridViewRow Gprev = GridView1.Rows[e.Row.RowIndex - 1];
                if (Gprev.Cells[0].Text.Equals(e.Row.Cells[0].Text))
                {
                    e.Row.Cells[0].Text = "";
                }
            }
            //now continue with the rest of the rows

            if (e.Row.RowIndex > 1)
            {
                //set reference to the row index and the current value
                int intC = e.Row.RowIndex;
                string lookfor = e.Row.Cells[0].Text;

                //now loop back through checking previous entries for matches
                do
                {
                   GridViewRow Gprev = GridView1.Rows[intC-1];

                    if (Gprev.Cells[0].Text.Equals(e.Row.Cells[0].Text))
                        {
                            e.Row.Cells[0].Text = "";
                        }

                  intC = intC - 1;
                } while (intC >0);

            }

        }

    }