using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var list1 = new List<int>{1, 2, 3, 6, 4};

        var list2 = new List<int>{4, 1, 2};

        var selection =

            from l1 in list1

            join l2 in list2 on l1 equals l2 into joined

            from j in joined.DefaultIfEmpty()select j;

        var depts = new List<Department>{new Department{Name = "Accounting"}, new Department{Name = "IT"}, new Department{Name = "Marketing"}};

        var persons = new List<Person>{new Person{DeptName = "Accounting", Name = "Bob"}};

        var selection2 =

            from d in depts

            join p in persons on d.Name equals p.DeptName into joined2

            from j2 in joined2.DefaultIfEmpty(new Person{DeptName = "Unknown", Name = "Alien"})select j2;

        foreach(var thisJ in selection2)

        {

            Console.WriteLine("Dept: {0}, Name: {1}", thisJ.DeptName, thisJ.Name);

        }

    }

​

    public class Person

    {

        public string Name

        {

            get;

            set;

        }

​

        public string DeptName

        {

            get;

            set;

        }

    }

​

    public class Department

    {

        public string Name

        {

            get;

            set;

        }

    }

}