LINQ操作符四：排序操作符

张小龙net馆藏 2018-01-31

展开全文

排序操作符，包括OrderBy、OrderByDescending、ThenBy、ThenByDescending和Reverse，提供了升序或者降序排序。

OrderBy操作符将序列中的元素按照升序排列。

注意：orderby必须在select之前出现,查询表达式最后只可能出现select或者groupby。

student类：

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Text;
 5 using System.Threading.Tasks;
 6 
 7 namespace 排序操作符
 8 {
 9     public class Student
10     {
11 
12         //姓名
13         public string Name { get; set; }
14         //成绩
15         public int Score { get; set; }
16         public int Order { get; set; }
17         //构造函数
18         public Student(string name, int score, int order)
19         {
20             this.Name = name;
21             this.Score = score;
22             this.Order = order;
23         }
24     }
25 }

teacher类：

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Text;
 5 using System.Threading.Tasks;
 6 
 7 namespace 排序操作符
 8 {
 9     /// <summary>
10     /// Teacher类
11     /// </summary>
12     public class Teacher
13     {
14         //姓名
15         public string Name { get; set; }
16         //学生集合
17         public List<Student> Students { get; set; }
18 
19         public Teacher(string name, List<Student> students)
20         {
21             this.Name = name;
22             this.Students = students;
23         }
24     }
25 }

Program：

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Text;
 5 using System.Threading.Tasks;
 6 
 7 namespace 排序操作符
 8 {
 9     class Program
10     {
11         static void Main(string[] args)
12         {
13             //使用集合初始化器初始化Teacher集合
14             List<Teacher> teachers = new List<Teacher> { 
15                new Teacher("徐老师",
16                new List<Student>(){
17                  new Student("宋江",80,1),
18                 new Student("卢俊义",95,2),
19                 new Student("朱武",45,3)
20                }
21                ),
22                 new Teacher("姜老师",
23                new List<Student>(){
24                  new Student("林冲",90,2),
25                 new Student("花荣",85,4),
26                 new Student("柴进",58,5)
27                }
28                ),
29                 new Teacher("樊老师",
30                new List<Student>(){
31                  new Student("关胜",100,6),
32                 new Student("阮小七",70,7),
33                 new Student("时迁",30,0)
34                }
35                )
36             };
37 
38             #region OrderBy
39             //OrderBy 表达式
40             var queryOrderBy = from t in teachers
41                                from s in t.Students
42                                where s.Score < 60
43                                orderby s.Order
44                                select s;
45             //方法
46             var query = teachers.SelectMany(p => p.Students).Where(s => s.Score < 60).OrderBy(s => s.Order).Select(s => s);
47             foreach (var item in queryOrderBy)
48             {
49                 Console.WriteLine("姓名:"+item.Name+",分数:"+item.Score);
50             }
51             foreach (var item in query)
52             {
53                 Console.WriteLine("姓名:" + item.Name + ",分数:" + item.Score);
54             } 
55             #endregion
56 
57             Console.ReadKey();
58         }
59     }
60 }

运行结果：

二、OrderByDescending

OrderByDescending操作符将序列中的元素按照降序排列。

示例：

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Text;
 5 using System.Threading.Tasks;
 6 
 7 namespace 排序操作符
 8 {
 9     class Program
10     {
11         static void Main(string[] args)
12         {
13             //使用集合初始化器初始化Teacher集合
14             List<Teacher> teachers = new List<Teacher> { 
15                new Teacher("徐老师",
16                new List<Student>(){
17                  new Student("宋江",80,1),
18                 new Student("卢俊义",95,2),
19                 new Student("朱武",45,3)
20                }
21                ),
22                 new Teacher("姜老师",
23                new List<Student>(){
24                  new Student("林冲",90,2),
25                 new Student("花荣",85,4),
26                 new Student("柴进",58,5)
27                }
28                ),
29                 new Teacher("樊老师",
30                new List<Student>(){
31                  new Student("关胜",100,6),
32                 new Student("阮小七",70,7),
33                 new Student("时迁",30,0)
34                }
35                )
36             };
37 
38             #region OrderByDescending
39             //表达式
40             var queryDesc = from t in teachers
41                             from s in t.Students
42                             where s.Score < 60
43                             orderby s.Order descending
44                             select s;
45             //方法
46             var query1 = teachers.SelectMany(p => p.Students).Where(s => s.Score < 60).OrderByDescending(s => s.Order).Select(s => s);
47             foreach (var item in queryDesc)
48             {
49                 Console.WriteLine("姓名:" + item.Name + ",分数:" + item.Score);
50             }
51             foreach (var item in queryDesc)
52             {
53                 Console.WriteLine("姓名:" + item.Name + ",分数:" + item.Score);
54             }
55             #endregion
56 
57             Console.ReadKey();
58         }
59     }
60 }

运行效果：

三、ThenBy排序

ThenBy操作符实现按照次关键字对序列进行升序排列。此操作符的查询语法和方法语法略有不同，例如：

//查询语法
var query=from e in Employees orderby e.FirstName,e.LastName select e;
//方法语法
var q=Employees.OrderBy(e=>e.FirstName).ThenBy(e=>e.LastName).Select(e=>e);

示例：

Category类：

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Text;
 5 using System.Threading.Tasks;
 6 
 7 namespace ThenBy
 8 {
 9     public class Category
10     {
11         public Guid CategoryId { get; set; }
12         public string CategoryName { get; set; }
13         public int Order { get; set; }
14     }
15 }

Products类：

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Text;
 5 using System.Threading.Tasks;
 6 
 7 namespace ThenBy
 8 {
 9     public class Products
10     {
11         public Guid Id { get; set; }
12         public Guid CategoryId { get; set; }
13         public string Name { get; set; }
14         public int Order { get; set; }
15         public DateTime CreateTime { get; set; }
16     }
17 }

Program:

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Text;
 5 using System.Threading.Tasks;
 6 
 7 namespace ThenBy
 8 {
 9     class Program
10     {
11         static void Main(string[] args)
12         {
13             List<Products> pro = new List<Products>() { 
14                new Products(){Id=Guid.NewGuid(),Name="格林童话",CategoryId=Guid.NewGuid(),Order=1,CreateTime=DateTime.Now.AddHours(2)},
15                new Products(){Id=Guid.NewGuid(),Name="美女与野兽",CategoryId=Guid.NewGuid(),Order=1,CreateTime=DateTime.Now},
16                new Products(){Id=Guid.NewGuid(),Name="世界如此险恶，您的内心需要强大",CategoryId=Guid.NewGuid(),Order=0,CreateTime=DateTime.Now.AddHours(3)}            
17             };
18             //查询语法
19             var query = (from p in pro orderby p.Order, p.CreateTime select p);
20             //方法
21             var q = pro.OrderBy(p => p.Order).ThenBy(p => p.CreateTime).Select(p => p);
22             foreach (var item in query)
23             {
24                 Console.WriteLine("name:"+item.Name+"id:"+item.Id+",order:"+item.Order+",CreateTime:"+item.CreateTime);
25             }
26             foreach (var item in q)
27             {
28                 Console.WriteLine("name:" + item.Name + "id:" + item.Id + ",order:" + item.Order + ",CreateTime:" + item.CreateTime);
29             }
30 
31             Console.ReadKey();
32         }
33     }
34 }

运行效果：

四、ThenByDescending

ThenByDescending操作符实现按照次关键字对序列进行降序排列。此操作符的查询语法与方法语法略有不同，例如：

//查询语法
var query=from e in Employees orderby e.FirstName,e.LastName descending select e;
//方法语法
var q=Employees.OrderBy(e=>e.FirstName).ThenByDescending(e=>e.LastName).Select(e=>e);

示例：

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Text;
 5 using System.Threading.Tasks;
 6 
 7 namespace ThenBy
 8 {
 9     class Program
10     {
11         static void Main(string[] args)
12         {
13             List<Products> pro = new List<Products>() { 
14                new Products(){Id=Guid.NewGuid(),Name="格林童话",CategoryId=Guid.NewGuid(),Order=1,CreateTime=DateTime.Now.AddHours(2)},
15                new Products(){Id=Guid.NewGuid(),Name="美女与野兽",CategoryId=Guid.NewGuid(),Order=1,CreateTime=DateTime.Now},
16                new Products(){Id=Guid.NewGuid(),Name="世界如此险恶，您的内心需要强大",CategoryId=Guid.NewGuid(),Order=0,CreateTime=DateTime.Now.AddHours(3)}            
17             };
18             //查询语法
19             var query = from p in pro orderby p.Order, p.CreateTime descending select p;
20             //方法
21             var q = pro.OrderBy(p => p.Order).ThenByDescending(p => p.CreateTime);
22             foreach (var item in query)
23             {
24                 Console.WriteLine("name:" + item.Name + "id:" + item.Id + ",order:" + item.Order + ",CreateTime:" + item.CreateTime);
25             }
26             foreach (var item in q)
27             {
28                 Console.WriteLine("name:" + item.Name + "id:" + item.Id + ",order:" + item.Order + ",CreateTime:" + item.CreateTime);
29             }
30 
31             Console.ReadKey();
32         }
33     }
34 }

运行效果：

五、Reverse

Reverse将会把序列中的元素按照从后到前的顺序反转。需要注意的是，Reverse方法的返回值是void,例如：

var q=Employees.Select(e=>e.FirstName).ToList();
q.Reverse();

示例：

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Text;
 5 using System.Threading.Tasks;
 6 
 7 namespace ThenBy
 8 {
 9     class Program
10     {
11         static void Main(string[] args)
12         {
13             string[] str = { "A", "B", "C", "D", "E"};
14             var query = str.Select(p => p).ToList();
15             query.Reverse();
16             foreach (var item in query)
17             {
18                 Console.WriteLine(item);
19             }
20 
21             Console.ReadKey();
22         }
23     }
24 }