c# group by list

 ViewBag.PnlTotal = pnlTotal;
            // 柱形图
            string data = "";
            string cat = "";
            string buyOrderTotalOrderAmount = "";


            var r = listReports.OrderBy(p => p.DateRange).ThenBy(p => p.VendorID).GroupBy(g => g.DateRange).Select(g =>
              new PnlDiagram
              {
                  Key = g.Key,
                  Value = string.Join(",", g.Select(c => c.VendorTotalPnL)),
                  BuyOrderTotalOrderAmount=string.Join(",",g.Select(p=>p.BuyOrderTotalOrderAmount)),
                  Partner = string.Join(",", g.Select(c => c.VendorID))
              });

           

            foreach (var item in r)
            {
                cat = item.Partner;
                data += "name:" + item.Key + "#data:[" + item.Value + "];";
                buyOrderTotalOrderAmount += "name:" + item.Key + "#data:[" + item.BuyOrderTotalOrderAmount + "];";
            }
            ViewBag.CatNew = cat;
            ViewBag.DataNew = data;
            ViewBag.BuyOrderTotalOrderAmount = buyOrderTotalOrderAmount;
            return PartialView("PNLReport_Partial", listReports);