how to filter the data

internal void WebServiceProxyMethod()
        {
            try
            {
                vocher = new Voucher();
                vocher.Credentials = new System.Net.NetworkCredential("MTL101", "MTLXXXX");
                XmlNode xmlnode = vocher.VoucherExport();

                XmlReader xmlReader = new XmlNodeReader(xmlnode);
                using (ds = new DataSet())
                {
                    ds.ReadXml(xmlReader);
                    DataTable dt = ds.Tables["TableName"];
                    if (dt != null)
                    {
                        foreach (DataRow dr in dt.Rows)
                        {

                        }
                    }
                }
            }