不管在c/s還是b/s的c#語言開發程序中，經常會用到List的擴展方法，尤其在json格式的數據和服務端交互越來越流行，很多時候總是在開發使用到的時候才去搜索有些擴展方法或者linq的用法，在這裡，我們只是做一個備注
因為linq沒有必要系統的學習，我們只要簡單的在list的擴展會使用即可，至少我只這麼認為的
本文沒有任何技術性，只是備注list或者list泛型的擴展方法，不至於在您不熟悉但是又使用到的時候到處搜索
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 //泛型方法的類型參數是可以省略的
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 //按照某一條件求和
27 double sumSalaryFilter = employees.Where<Employee>(e => e.Name == "Bob").ToList().Sum(e => e.Salary);//12.0
28 //【linq方式】按照某一條件求和
29 var sumSalaryFilter2 = (from v in employees where v.Name == "Bob" select v).Sum(e => e.Salary);//12.0
30
31 //選擇數據而已，即返回自定義改變後的新的投影的數據列表（無法改變源數據）
32 var selectChangedNameList = employees.Select<Employee, Employee>(e => { return new Employee { Name = "Bob" }; }).ToList();
33 //【linq方式】選擇數據而已，即返回自定義改變後的新的投影的數據列表（無法改變源數據）
34 var selectChangedNameList2 = (from v in employees select new { Name = "Bob", Salary = v.Salary, Dependents = v.Dependents }).ToList();
35 //選擇返回某一列的清單投影的數據列表
36 var selectSalaryList = employees.Select<Employee, double>(e => { return e.Salary; }).ToList();
37
38 //查找符合條件的第一個元素
39 Employee employee1 = employees.Find(e => e.Name == "Bob");
40 //【linq方式】查找符合條件的第一個元素
41 Employee employee2 = (from v in employees where v.Name == "Bob" select v).First();
42 //不用lambda方式篩選符合條件的元素列表
43 Predicate<Employee> aaaa = new Predicate<Employee>(fun1);
44 List<Employee> employee1List = employees.FindAll(aaaa);
45 //lambda方式篩選符合條件的元素列表
46 List<Employee> employee2List = employees.FindAll(e => e.Name == "Bob");
47 //【linq方式】方式篩選符合條件的元素列表
48 List<Employee> employee2List2 = (from v in employees where v.Name == "Bob" select v).ToList();
49 //max，min，平均值，篩選滿足某條件的max和min已經使用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 //簡單的運算，比如列表總的相加的值
56 var aggregateEmployee = employees.Aggregate<Employee>((result, next) => new Employee { Salary = result.Salary + next.Salary });
57 //某一列的不重復的匯總
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 //查詢滿足某一條件的所有數據
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 }
