List扩展方法汇总（仅备注）_.NET_编程开发_程序员俱乐部

不管在c/s还是b/s的c#语言开发程序中，经常会用到List的扩展方法，尤其在json格式的数据和服务端交互越来越流行，很多时候总是在开发使用到的时候才去搜索有些扩展方法或者linq的用法，在这里，我们只是做一个备注

因为linq没有必要系统的学习，我们只要简单的在list的扩展会使用即可，至少我只这么认为的

本文没有任何技术性，只是备注list或者list泛型的扩展方法，不至于在您不熟悉但是又使用到的时候到处搜索

 1  public sealed class Employee
 2     {
 3         public string Name { get; set; }
 4         public double Salary { get; set; }
 5         public short Dependents { get; set; }
 6     }
 7     public class Test
 8     {
 9         public void FunTest()
10         {
11             var employees = new List<Employee>
12              {
13                     new Employee { Name = "Bob", Salary = 1, Dependents = 0 },
14                     new Employee { Name = "Sherry", Salary = 2, Dependents = 1 },
15                     new Employee { Name = "Kathy", Salary = 3, Dependents = 0 },
16                     new Employee { Name = "Joe", Salary = 4, Dependents = 2 },
17                     new Employee { Name = "Bob", Salary = 5, Dependents = 0 },
18                     new Employee { Name = "Bob", Salary = 6, Dependents = 0 }
19              };
20             //泛型方法的类型参数是可以省略的
21 
22             //所有求和
23             double sumSalary = employees.Sum<Employee>(e => e.Salary);//21.0
24             //【linq方式】所有求和
25             var sumSalary2 = (from v in employees select v).Sum(e => e.Salary);//21.0


26             //按照某一条件求和
27             double sumSalaryFilter = employees.Where<Employee>(e => e.Name == "Bob").ToList().Sum(e => e.Salary);//12.0
28             //【linq方式】按照某一条件求和
29             var sumSalaryFilter2 = (from v in employees where v.Name == "Bob" select v).Sum(e => e.Salary);//12.0
30 

31             //选择数据而已，即返回自定义改变后的新的投影的数据列表（无法改变源数据）
32             var selectChangedNameList = employees.Select<Employee, Employee>(e => { return new Employee { Name = "Bob" }; }).ToList();
33             //【linq方式】选择数据而已，即返回自定义改变后的新的投影的数据列表（无法改变源数据）
34             var selectChangedNameList2 = (from v in employees select new { Name = "Bob", Salary = v.Salary, Dependents = v.Dependents }).ToList();
35             //选择返回某一列的清单投影的数据列表
36             var selectSalaryList = employees.Select<Employee, double>(e => { return e.Salary; }).ToList();
37 

38             //查找符合条件的第一个元素
39             Employee employee1 = employees.Find(e => e.Name == "Bob");
40             //【linq方式】查找符合条件的第一个元素
41             Employee employee2 = (from v in employees where v.Name == "Bob" select v).First();
42             //不用lambda方式筛选符合条件的元素列表
43             Predicate<Employee> aaaa = new Predicate<Employee>(fun1);
44             List<Employee> employee1List = employees.FindAll(aaaa);
45             //lambda方式筛选符合条件的元素列表
46             List<Employee> employee2List = employees.FindAll(e => e.Name == "Bob");
47             //【linq方式】方式筛选符合条件的元素列表
48             List<Employee> employee2List2 = (from v in employees where v.Name == "Bob" select v).ToList();


49             //max，min，平均值，筛选满足某条件的max和min已经使用linq方式
50             employees.Max(e => e.Salary);
51             employees.Min(e => e.Salary);
52             (from v in employees select v).Max(e => e.Salary);
53             (from v in employees select v).Min(e => e.Salary);
54             double maxSalaryFilter = employees.Where<Employee>(e => e.Name == "Bob").ToList().Max(e => e.Salary);

55             //简单的运算，比如列表总的相加的值
56             var aggregateEmployee = employees.Aggregate<Employee>((result, next) => new Employee { Salary = result.Salary + next.Salary });


57             //某一列的不重复的汇总
58             var groupEmployees = employees.GroupBy(e => new { e.Name }).Select(g => new { g.Key, Count = g.Count() }).ToList();
59             var groupEmployees1 = employees.GroupBy(e => e.Name).Select(e => new { Name = e.Key, sumSalary = e.Sum(d => d.Salary) }).ToList();
60             var groupEmployees2 = (from v in employees group v by v.Name into g select new { Name = g.Key, SumSalary = g.Sum(d => d.Salary) }).ToList();


61             //查询满足某一条件的所有数据
62             IEnumerable<Employee> employee3List = employees.Where<Employee>(e => e.Name == "Bob");
63             List<Employee> employee4List = employees.Where<Employee>(e => e.Name == "Bob").ToList();
64             employee3List = employee4List as IEnumerable<Employee>;
65 
66             Console.WriteLine("adfadsfasdfasdf");
67         }
68 
69 
70         private bool fun1(Employee e)
71         {
72             return (e.Name == "Bob");
73         }
74     }