Linq to Sql多列分组

var groupByList = from items in list  
                            group items by new
                            {
                                      items.TargetCompanyId,//分组的字段
                                      items.TargetCompanyName,
                                      items.ExamItemType,
                                      items.ProcessId,
                                      items.ProcessName,
                                      items.TargetOptionId,
                                      items.TargetOptionName,
                                      items.EngUnitId,
                                      items.Ranking
                                  } into c
                                  select new
                                  {//显示的字段
                                      c.Key.TargetCompanyId,
                                      c.Key.TargetCompanyName,
                                      c.Key.ExamItemType,
                                      c.Key.ProcessId,
                                      c.Key.ProcessName,
                                      c.Key.TargetOptionId,
                                      c.Key.TargetOptionName,
                                      c.Key.EngUnitId,
                                      c.Key.Ranking,
                                      ExamValue = c.Average(g =>            g.ExamValue)//根据分组的字段求和或者求平均值
                                  };