check ค่าใน gridview ... อยากทราบวิธีเช็คค่าซ้ำใน gridview ว่าซ้ำกันไหม

    private int Num = 0;

    protected void Page_Load(object sender, EventArgs e)
    {
        GridView1.RowDataBound += new GridViewRowEventHandler(GridView1_RowDataBound);
    }

    private void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
    {
        if (e.Row.RowType == DataControlRowType.DataRow)
        {
            if (Num == int.Parse(e.Row.Cells[0].Text))
            {
                e.Row.Cells[0].Text = "-";
            }
            else
            {
                Num = int.Parse(e.Row.Cells[0].Text);
            }
        }
    }