C#联接序列

1.  Concat() – 串联序列（有重复项）

 var healthFoods = new List<string> { "fruits", "vegetables", "grains", "proteins" };

 var myFoods = new List<string> { "grains", "proteins", "M&Ms", "soda" };

 var healthyFirst = healthFoods.Concat(myFoods); // 返回序列: fruits, vegetables, grains, proteins, grains, proteins, M&Ms, soda

var mineFirst = myFoods.Concat(healthFoods);// 返回序列: grains, proteins, M&Ms, soda, fruits, vegetables, grains, proteins

2. Union() – 串联序列（无重复项）

 var healthyFirst = healthFoods.Union(myFoods);// 返回序列: fruits, vegetables, grains, proteins, M&Ms, soda

 var mineFirst = myFoods.Union(healthFoods);// 返回序列: grains, proteins, M&Ms, soda, fruits, vegetables

3.Zip() – 简单一对一的联接（注：Employee 和Seat是两个对象）

var employees = new List<Employee>

    {

         new Employee { Id = 13, Name = "John Doe", Salary = 13482.50 },
         new Employee { Id = 42, Name = "Sue Smith", Salary = 98234.13 },
         new Employee { Id = 99, Name = "Jane Doe", Salary = 32421.12 }

     };

 var seats = new List<Seat>
     {
         new Seat { Id = 1, Cost = 42 },
         new Seat { Id = 2, Cost = 42 },
         new Seat { Id = 3, Cost = 100 },
         new Seat { Id = 4, Cost = 100 },
         new Seat { Id = 5, Cost = 125 },
         new Seat { Id = 6, Cost = 125 },
     };

//接下来使用Zip（）

var seatingAssignments = employees.Zip(seats, (e, s) => new { EmployeeId = e.Id, SeatId = s.Id });
 foreach (var seat in seatingAssignments)
 {
     Console.WriteLine("雇员: " + seat.EmployeeId + " 预约了座位 " + seat.SeatId);
 
 }     

//运行结果（注：一旦到达较短序列的最后一项，它就会立即停止）

雇员: 13 预约了座位1

雇员: 42 预约了座位2

雇员: 99 预约了座位3

4.Join() – 满足条件的联接(注：Employee和Badge是两个对象)

var employees = new List<Employee>
     {
         new Employee { Id = 13, Name = "John Doe", Salary = 13482.50 },
         new Employee { Id = 42, Name = "Sue Smith", Salary = 98234.13 },
         new Employee { Id = 99, Name = "Jane Doe", Salary = 32421.12 }
     };
 var badges = new List<Badge>
     {
         new Badge { EmployeeId = 10, BadgeNumber = 1 },
         new Badge { EmployeeId = 13, BadgeNumber = 2 },
         new Badge { EmployeeId = 20, BadgeNumber = 3 },
         new Badge { EmployeeId = 25, BadgeNumber = 4 },
         new Badge { EmployeeId = 42, BadgeNumber = 5 },
         new Badge { EmployeeId = 10, BadgeNumber = 6 },
         new Badge { EmployeeId = 13, BadgeNumber = 7 },
     };

//接下来使用Join()

var badgeAssignments = employees.Join(badges, e => e.Id, b => b.EmployeeId,  (e, b) => new { e.Name, b.BadgeNumber });

 foreach (var badge in badgeAssignments)
 {
     Console.WriteLine("Name: " + badge.Name + " has badge " + badge.BadgeNumber);
 }   

返回结果：（注：不会返回Jane Doe的信息）
 Name: John Doe has badge 2
 Name: John Doe has badge 7
 Name: Sue Smith has badge 5

5.GroupJoin() – 适用于一对多的条件联接

var badgeAssignments = employees.GroupJoin(b adges, e => e.Id, b => b.EmployeeId, (e, bList) => new { Name = e.Name, Badges = bList.ToList() }); 

foreach (var assignment in badgeAssignments) 
{
   Console.WriteLine(assignment.Name + " has badges:"); 

   if (assignment.Badges.Count > 0) 
   {

         foreach (var badge in assignment.Badges)
         {
             Console.WriteLine("\tBadge: " + badge.BadgeNumber);
         } 
   } 
   else {

       Console.WriteLine("\tNo badges.");

   }
} 

//输出结果

John Doe has badges:

         Badge: 2

         Badge: 7

 Sue Smith has badges:

         Badge: 5

 Jane Doe has badges:

         No badges.