using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public class Employee{

        public int Id {get;set;}

        public string Name {get;set;}

        public int DeptId {get;set;}

    }

    public class Department{

        public int Id {get;set;}

        public string Name {get;set;}

    }

    public static void Main()

    {

        var departments  = new List<Department>();

        departments.Add(new Department{

            Id =1,

            Name = "AAA"            

        });

        departments.Add(new Department{

            Id =2,

            Name = "BBB"            

        });

        departments.Add(new Department{

            Id =3,

            Name = "CCC"            

        });

        departments.Add(new Department{

            Id =4,

            Name = "DDD"            

        });

        var employees  = new List<Employee>();

        employees.Add(new Employee{

            Id =1,

            Name = "XXX",

            DeptId = 1

        });

        employees.Add(new Employee{

            Id =2,

            Name = "YYY",

            DeptId = 2

        });

        employees.Add(new Employee{

            Id =3,

            Name = "ZZZ",

            DeptId = 3

        });

        employees.Add(new Employee{

            Id =4,

            Name = "KKK",

            DeptId = 4

        });

        employees.Add(new Employee{

            Id =5,

            Name = "UUU",

            DeptId = 1

        });

        employees.Add(new Employee{

            Id =6,

            Name = "TTT",

            DeptId = 2

        });

        //perform a query on departments with more then 2 employees

        var deptnames = departments.Join(employees , dept => dept.Id, emp=>emp.DeptId, (dept,emp) => new {Department = dept, Employee = emp})           

            .GroupBy(x=>x.Department).Select(x=>new {x.Key.Name , Count =  x.Count()});

        deptnames.Dump();

    }

}