data table comma separated values

Dictionary<string, StringBuilder> dict = new Dictionary<string, StringBuilder>();
foreach (DataRow row in dt.Rows)
    {
    string msg = (string)row["MSG"];
    string to = (string)row["TO"];
    if (!dict.ContainsKey(msg))
        {
        dict.Add(msg, new StringBuilder(to));
        }
    else
        {
        dict[msg].AppendFormat(",{0}", to);
        }
    }
foreach (string key in dict.Keys)
    {
    Console.WriteLine("{0} {2}", key, dict[key].ToString());
    }