合並相同的行(記錄)

DataTable dt = new DataTable();
   dt.Columns.Add("f");
   dt.Columns.Add("t");
   DataRow row = dt.NewRow();
   row[0] = "aa";
   row[1] = "10";
   dt.Rows.Add(row);
   row = dt.NewRow();
   row[0] = "bb";
   row[1] = "20";
   dt.Rows.Add(row);
   row = dt.NewRow();
   row[0] = "cc";
   row[1] = "20";
   dt.Rows.Add(row);
   row = dt.NewRow();
   row[0] = "aa";
   row[1] = "15";
   dt.Rows.Add(row);
   row = dt.NewRow();
   row[0] = "bb";
   row[1] = "-10";
   dt.Rows.Add(row);
   DataTable dtTemp = dt.Clone();
   for(int i=0; i<dt.Rows.Count;i++)
   {
    DataRow[] rrow = dtTemp.Select("f=''"+dt.Rows[i]["f"].ToString()+"''");
    if(rrow.Length > 0)
    {
     dtTemp.Select("f=''"+dt.Rows[i]["f"].ToString()+"''")[0][1] = int.Parse(dtTemp.Select("f=''"+dt.Rows[i][0].ToString()+"''")[0][1].ToString()) + int.Parse(dt.Rows[i][1].ToString());                  
     dtTemp.AcceptChanges();
    }
    else
    {
     DataRow dr = dtTemp.NewRow();
     dr[0] = dt.Rows[i][0].ToString();
     dr[1] = dt.Rows[i][1].ToString();
     dtTemp.Rows.Add(dr);
    }