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List扩展方法汇总(仅备注)

时间:2014-11-18 23:46:17      阅读:314      评论:0      收藏:0      [点我收藏+]

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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 }

 

List扩展方法汇总(仅备注)

标签:style   blog   ar   color   使用   sp   数据   div   on   

原文地址:http://www.cnblogs.com/yinhaichao/p/4106588.html

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