Linq GroupBy with Aggregate functions

 List<Employee> empList = new List<Employee>();  
       empList.AddRange(new Employee[]   
       {   
         new Employee {EmpId =1, DeptId=1, Position="Director", Salary=100 },  
         new Employee {EmpId =2, DeptId=1, Position="Director", Salary = 120},  
         new Employee {EmpId =3, DeptId=1, Position="Software Engineer", Salary=50 },  
         new Employee {EmpId =4, DeptId=2, Position="Director", Salary=90 },  
         new Employee {EmpId =5, DeptId=2, Position="Director", Salary=100 },  
         new Employee {EmpId =6, DeptId=3, Position="HR Assistant", Salary=40 },  
         new Employee {EmpId =7, DeptId=3, Position="HR Manager", Salary=70},  
         new Employee {EmpId =8, DeptId=4, Position="IT Manager", Salary=85 },  
         new Employee {EmpId =8, DeptId=4, Position="IT Assistant", Salary=40 }  
       });  
   
       /*  
        * The highest salary from the each dept per position  
       */  
       empList.GroupBy(_ => new { _.DeptId, _.Position })  
         .Select(_ => new  
         {  
           MaximumSalary = _.Max(deptPositionGroup => deptPositionGroup.Salary),  
           DepartmentId = _.Key.DeptId,  
           Position = _.Key.Position  
         }).ToList()  
         .ForEach(selectedRecords =>  
         {  
           Console.WriteLine("{0} {1} {2}", selectedRecords.DepartmentId, selectedRecords.Position, selectedRecords.MaximumSalary);  
         });  
   
       /*Average salary from each dept per position */  
   
       Console.WriteLine();  
       Console.WriteLine();  
       Console.WriteLine();  
       empList.GroupBy(_ => new { _.DeptId, _.Position })  
               .Select(_ => new  
               {  
                 AverageSalary = _.Average(deptPositionGroup => deptPositionGroup.Salary),  
                 DepartmentId = _.Key.DeptId,  
                 Position = _.Key.Position  
               }).ToList()  
               .ForEach(selectedRecords =>  
               {  
                 Console.WriteLine("{0} {1} {2}", selectedRecords.DepartmentId, selectedRecords.Position, selectedRecords.AverageSalary);  
               });  
       Console.WriteLine();  
       Console.WriteLine();  
       Console.WriteLine();  
       /*Average salary from each dept */  
       empList.GroupBy(_ => _.DeptId)  
               .Select(_ => new  
               {  
                 AverageSalary = _.Average(deptPositionGroup => deptPositionGroup.Salary),  
                 DepartmentId = _.Key,  
               }).ToList()  
               .ForEach(selectedRecords =>  
               {  
                 Console.WriteLine("{0} {1}", selectedRecords.DepartmentId, selectedRecords.AverageSalary);  
               });