Add selected Rows into Datatable from DataSet

  DataSet ds = new DataSet();
  ds = (DataSet)Session["dsFocusArea"];
  DataTable dt = ds.Tables[1].Clone();
  foreach (DataRow row in ds.Tables[1].Select("unitid = " + TextBox1.Text + ""))
  {
    dt.Rows.Add(row.ItemArray);
  }