Linq 中按照多个值进行分组(GroupBy) .GroupBy(x => new { x.Age, x.Sex }) group emp by new { emp.Age, emp.Sex } into g   // 实现多key分组的扩展函数版本 var sums = empList          .GroupBy(x => new { x.Age, x.Sex })          .Select(group => new {             Peo = group.Key, Count = group.Count()          }); foreach (var employee in sums) {    Console.WriteLine(employee.Count + ": " + employee.Peo); }  // 实现多key分组的lambda版本 var sums2 = from emp in empList             group emp by new { emp.Age, emp.Sex } into g             select new { Peo = g.Key, Count = g.Count() }; foreach (var employee in sums) {    Console.WriteLine(employee.Count + ": " + employee.Peo); }