Avoid Duplicate Records in GridView Dynamically

protected void gvDemo_RowDataBound(object sender, EventArgs e)
{
    string szOldVal = "";
    string szNewVal = "";
    for (int iRowCount = 0; iRowCount < gvList.Rows.Count; iRowCount++)
     {
            szOldVal = gvList.Rows[count].Cells[iRowCount].Text.Trim();
            if (szOldVal == szNewVal)
            {
                gvDemo.Rows[count].Visible = false;
            }
            szNewVal = szOldVal;
     }
}

DataRow[] col=dt.Select("your condition");
if(col.Count == 0)
{
       //insert record into temp table and store the same in viewstate again
}

 string oldValue = string.Empty;
    string newValue = string.Empty;
    for (int j = 0; j < 2; j++)
    {
        for (int count = 0; count < gvList.Rows.Count; count++)
        {
            oldValue = gvList.Rows[count].Cells[j].Text;
            if (oldValue == newValue)
            {
                gvList.Rows[count].Cells[j].Text = string.Empty;
            }
            newValue = oldValue;
        }
    }

protected void RemoveDuplicates(object sender, EventArgs e)
{
    DataTable dt = (DataTable)ViewState["dt"];
    dt = dt.DefaultView.ToTable(true, "Id", "Name", "Country");
    GridView1.DataSource = dt;
    GridView1.DataBind();
}