c# Lambda表达式结合Linq的学习整理

蔚落 2021-10-23 09:59 462阅读 0赞

学习整理！

定义基础类

/// <summary>
        /// 球员类
        /// </summary>
        public class Player
        {
            public int ID { get; set; }
    
            public string Name { get; set; }
    
            public int Age { get; set; }
    
            /// <summary>
            /// 所属位置
            /// </summary>
            public Location Location { get; set; }
    
            /// <summary>
            /// 所属球队
            /// </summary>
            public Team Team { get; set; }
    
            public int MvpNumber { get; set; }
    
        }

/// <summary>
        /// 位置类
        /// </summary>
        public class Location
        {
    
            public string LocationCode { get; set; }
    
            public string LocationName { get; set; }
        }
    }

/// <summary>
        /// 球队类
        /// </summary>
        public class Team
        {
            public string TeamCode { get; set; }
    
            public string TeamName { get; set;  }
        }

添加数据

//初始化测试数据
                List<Player> players = new List<Player>()
                {
                    new Player { ID = 1, Name = "Harden", Age = 30,
                        Location = new Location { LocationCode = "PG", LocationName = "控球" },
                        Team = new Team { TeamCode = "HOU", TeamName = "休斯顿火箭" }, MvpNumber = 1
                    },
                       new Player { ID = 2, Name = "Curry", Age = 29,
                        Location = new Location { LocationCode = "SG", LocationName = "得分" },
                        Team = new Team { TeamCode = "GSW", TeamName = "金州勇士" }, MvpNumber = 2
                    },
                          new Player { ID = 3, Name = "James", Age = 33,
                        Location = new Location { LocationCode = "SF", LocationName = "小前" },
                        Team = new Team { TeamCode = "LAL", TeamName = "洛杉矶湖人" }, MvpNumber = 5
                    },
                             new Player { ID = 4, Name = "Zhouqi", Age = 20,
                        Location = new Location { LocationCode = "PF", LocationName = "大前" },
                        Team = new Team { TeamCode = "CHN", TeamName = "铁头娃队" }, MvpNumber = 0
                    },
                                new Player { ID = 5, Name = "Yao", Age = 36,
                        Location = new Location { LocationCode = "C", LocationName = "中锋" },
                        Team = new Team { TeamCode = "CHN", TeamName = "无敌天朝队" }, MvpNumber = 8
                    }
                };

开始测试

引入 using System.Linq;

一、Max/Min(最大值/最小值)

var ageMax = players.Max(u => u.Age);
                Console.WriteLine("最大年龄:" + ageMax);
    
                var ageMin = players.Min(u => u.Age);
                Console.WriteLine("最小年龄:" + ageMin);

结果：![1574889-20190706161929649-1594308717.png][]

二、Where条件筛选

Method 1 ：源数据.Where( u => u.属性 筛选条件);

Method 2：from 变量 in 源数据

Where 变量.属性 筛选条件

Select 变量;

ps: 可加ToList()方法带出数据(个人比较Low的解释)

//查询MvpNumber值大于2的球员
                //第一种写法
                var mvpNum1 = players.Where(u => u.MvpNumber > 2).ToList();  
    
                //第二种写法
                var mvpNum2 = (from n in players
                               where n.MvpNumber > 2
                               select n).ToList();

输出:![1574889-20190706164614272-236025204.png][]

三、排序 OrderBy

升序：源数据.OrderBy( u => u.属性).ToList();

降序：源数据.OrderByDescending( u => u.属性).ToList();

ps:必须包含ToList()方法,否则报类型错误

//按年龄升序排序
                players = players.OrderBy(u => u.Age).ToList();
                //按年龄降序排序
                players = players.OrderByDescending(u => u.MvpNumber).ToList();

结果：![1574889-20190706170433954-1764377432.png][]

四、分组GroupBy

Method 1：源数据.GroupBy( u => u.属性).ToList();

Method 2：from n in 源数据

group n by n.属性

into newGroup

Select newGroup;

//按球队分组
                Console.WriteLine("\n方法一：");
    
                var teamGroup = players.GroupBy(u => u.Team.TeamName).ToList();
    
                Console.WriteLine("共有{0}支球队", teamGroup.Count());
                foreach (var item in teamGroup)
                {
                    Console.WriteLine("球队名称：{0}", item.Key);
    
                    foreach (var n in item)
                    {
                        Console.WriteLine(n.ID + "\t" + n.Name + "\t" + n.Age + "\t" +
                            n.Location.LocationCode + "\t" + n.Location.LocationName + "\t" +
                            n.Team.TeamCode + "\t" + n.Team.TeamName + "\t" + n.MvpNumber);
                    }
                }
    
           
                Console.WriteLine("\n方法二：");
    
                var teamGroup2 = (from n in players
                                  group n by n.Team.TeamName
                         　　　　　　into newGroup
                                  select newGroup).ToList();
    
                Console.WriteLine("共有{0}支球队", teamGroup2.Count());
                foreach (var item in teamGroup2)
                {
                    Console.WriteLine("球队名称：{0}", item.Key);
    
                    foreach (var n in item)
                    {
                        Console.WriteLine(n.ID + "\t" + n.Name + "\t" + n.Age + "\t" +
                            n.Location.LocationCode + "\t" + n.Location.LocationName + "\t" +
                            n.Team.TeamCode + "\t" + n.Team.TeamName + "\t" + n.MvpNumber);
                    }
                }

结果：![1574889-20190706175706481-1947129906.png][]

Linq Group By 用法总结

Key、Count

var q = (from n in players
                         group n by n.Team.TeamName
                         into g
                         select g).ToList();
    
    
                Console.WriteLine("\n共{0}支球队", q.Count()); //如果上面进行ToList操作，q.Count可以不加();
                foreach (var item in q)
                {
                    Console.WriteLine("球队名称：" + item.Key);
                }

结果：![1574889-20190708095037480-1516475769.png][] ![1574889-20190708095152865-1716060990.png][]

Group By中使用Where约束

//30岁以上年龄段分组
                var q = (from n in players
                        group n by n.Age
                        into g
                        where g.Key > 30
                        select g).ToList();

结果：![1574889-20190708094634368-1122481410.png][]

Group By根据表达式分组

//年龄大于30岁且MVP数量大于1分为一组，否则分在另一组
                var q = (from n in players
                         group n by n.Age > 30 && n.MvpNumber >= 1
                        into g
                         select g).ToList();
                foreach (var item in q)
                {
    
                    if (item.Key)
                    {
                        Console.WriteLine("满足条件:");
                        foreach (var n in item)
                        {
                            Console.WriteLine(n.ID + "\t" + n.Name + "\t" + n.Age + "\t" + 
                                n.Location.LocationCode + "\t" + n.Location.LocationName + "\t" +
                                n.Team.TeamCode + "\t" + n.Team.TeamName + "\t" + n.MvpNumber);
                        }
                    }
                    else
                    {
                        Console.WriteLine("不满足条件:");
                        foreach (var n in item)
                        {
                            Console.WriteLine(n.ID + "\t" + n.Name + "\t" + n.Age + "\t" +
                            n.Location.LocationCode + "\t" + n.Location.LocationName + "\t" +
                            n.Team.TeamCode + "\t" + n.Team.TeamName + "\t" + n.MvpNumber);
                        }
                    }
                }

结果：![1574889-20190708115453824-1489842462.png][]

输出：![1574889-20190708115640454-1151634974.png][]

Group By 多列

var q = (from n in players
                         group n by new
                         {
                             //这里的Key包含Age，Name以及Team信息
                             n.Age,
                             n.Name,
                             n.Team
                         }
                        into g
                         select g).ToList();

结果：![1574889-20190708133954653-80604957.png][]

ego cogito ergo sum!

转载于:https://www.cnblogs.com/junweiTang/p/11143594.html

[1574889-20190706161929649-1594308717.png]: /images/20211023/85f35e4276bd48228b07fe822cda04e3.png
[1574889-20190706164614272-236025204.png]: /images/20211023/c52017567455475dbf559a7791b0089b.png
[1574889-20190706170433954-1764377432.png]: /images/20211023/a23228d5d716448a9e76663fcde74216.png
[1574889-20190706175706481-1947129906.png]: /images/20211023/d3a7e5104f734ccc9488573179385ad2.png
[1574889-20190708095037480-1516475769.png]: https://img2018.cnblogs.com/blog/1574889/201907/1574889-20190708095037480-1516475769.png
[1574889-20190708095152865-1716060990.png]: /images/20211023/50351b5df712455e92911f3117816246.png
[1574889-20190708094634368-1122481410.png]: /images/20211023/b218c297788d4f4cab24fe04265eae6e.png
[1574889-20190708115453824-1489842462.png]: /images/20211023/3e1d2dc581594beab0ddec6ddf350247.png
[1574889-20190708115640454-1151634974.png]: /images/20211023/d08c224bfd0646c49b3f1bbb796493dd.png
[1574889-20190708133954653-80604957.png]: /images/20211023/81b43e4197e545ecb7c78c435e0044a9.png