從LINQ開始之LINQ to Objects（上）

LINQ概述

LINQ，語言集成查詢(Language Integrated Query)，它容許使用C#或VB代碼以查詢數據庫相同的方式來操做不一樣的數據源。

1.LINQ體系結構

從上圖能夠看出，LINQ總共包括五個部分：LINQ to Objects、LINQ to DataSets、LINQ to SQL、LINQ to Entities、LINQ to XML。

LINQ to Objects：對內存中集合的操做

LINQ to DataSets：對數據集Datatable的操做

LINQ to SQL：對SQL Server數據源的操做，微軟把開發的重點從LINQ to SQL轉移到了LINQ to Entities而且宣佈LINQ to SQL再也不提供更新

LINQ to Entities：是 Entity Framework的一部分而且取代LINQ to SQL做爲在數據庫上使用 LINQ的標準機制

LINQ to XML：對XML數據源的操做

2.LINQ的語法

下面是一個簡單的示例，查詢一個int數組中小於5的元素，並按照從小到大的順序排列：

int[] arr = new int[] { 1, 4, 2, 6, 7, 9, 5, 1, 2, 4 }; var query = from r in arr where r < 5 orderby r select r; foreach (var item in query) { Console.WriteLine(item); } Console.ReadLine();

由此示例能夠看出：LINQ查詢表達式以from子句開頭，以select子句結束。在兩個子句之間，可使用where、orderby等查詢操做符。

LINQ有兩種語法：Lambda語法和Query語法，編譯器會在程序編譯時轉換LINQ查詢，以調用相應的擴展方法。

如下是LINQ表達式結構示意圖：

引用自百度百科

LINQ to Objects

LINQ to Objects中的擴展方法在System.Core程序集的System.Linq命名空間中定義。

1.Enumerable類定義的標準查詢操做符：

下面介紹使用這些操做符的示例：

首先，咱們須要建立基本的實體類Employee：

/// <summary> /// 員工類 /// </summary> public class Employee { //員工編號 public string EmployeeId { get; private set; } //員工姓名 public string EmployeeName { get; private set; } //年齡 public int Age { get; private set; } //入職日期 public DateTime EntryDate { get; private set; } //性別 public string Sex { get; private set; } //部門 public string Department { get; private set; } //薪水 public int Salary { get; private set; } //愛好 public IEnumerable<string> Hobby { get; private set; } public Employee(string employeeId, string employeeName, int age, DateTime entryDate, Sex sex, Department department, int salary, IEnumerable<string> hobby) { this.EmployeeId = employeeId; this.EmployeeName = employeeName; this.Age = age; this.EntryDate = entryDate; this.Sex = sex.ToString(); this.Department = department.ToString(); this.Salary = salary; this.Hobby = hobby; } } //性別 public enum Sex { Male, Female } //部門 public enum Department { HR, IT, PD, FD, QC, MD }

而後,建立列表employees保存10名員工的基本信息：

List<Employee> employees = new List<Employee>() { new Employee("001","Mike",32,new DateTime(2016,2,20),Sex.Male,Department.IT,200000,new string[] { "swimming","shopping"}), new Employee("002","Jack",38,new DateTime(2007,5,12),Sex.Male,Department.HR,409989,new string[] { "reading"}), new Employee("003","Adolph",25,new DateTime(2017,3,23),Sex.Male,Department.IT,100000,new string[] { "play computer games","watch TV","listen to music"}), new Employee("004","Antony",30,new DateTime(2010,11,20),Sex.Male,Department.FD,320000, new string[] { "play chess","run"}), new Employee("005","Asa",28,new DateTime(2014,10,10),Sex.Female,Department.FD,120000,new string[] { "shopping"}), new Employee("006","Bernie",31,new DateTime(2008,4,5),Sex.Male,Department.PD,220000,new string[] { "play basketball"}), new Employee("007","Carl",26,new DateTime(2015,1,30),Sex.Male,Department.QC,100000,new string[] { "play chess","go fishing"}), new Employee("008","Duncan",30,new DateTime(2009,6,9),Sex.Male,Department.MD,250000,new string[] { "play computer games"}), new Employee("009","Aimee",24,new DateTime(2017,1,20),Sex.Female,Department.HR,80000,new string[] { "reading","run"}), new Employee("010","Cassie",31,new DateTime(2014,3,3),Sex.Female,Department.IT,350000,new string[] { "watch TV" }) };

1）篩選操做符（Where、OfType<TResult>）

Where：根據表達式函數過濾元素

//查詢年齡大於30歲，IT或HR部門全部員工的編號及姓名
        var filter = from r in employees where r.Age > 30 && (r.Department == Department.IT.ToString() || r.Department == Department.HR.ToString()) select r; foreach (var item in filter) { Console.WriteLine("EmployId: " +item.EmployeeId + " EmployeeName: " + item.EmployeeName); } //******************************Output******************************* //EmployId: 001 EmployeeName: Mike //EmployId: 002 EmployeeName: Jack //EmployId: 010 EmployeeName: Cassie //*******************************************************************

OfType<TResult>：類型篩選

//篩選出指定數組中全部int類型的元素
        object[] data = { "One", 2, 3, "Four", "Five", 6 }; var typeFilter = data.OfType<int>(); foreach (var item in typeFilter) { Console.WriteLine(item); } //******************************Output******************************* //2 //3 //6 //*******************************************************************

2）投射操做符（Select、SelectMany）

Select：根據選擇器函數選擇的結果值投射到新的類型元素上

SelectMany：C#編譯器把複合的from子句和LINQ查詢轉換爲SelectMany擴展方法，用於迭代序列的序列。

//查找我的愛好中有reading的員工的姓名
        var doubleFrom = from r in employees from h in r.Hobby where h == "reading" select r.EmployeeName; foreach (var item in doubleFrom) { Console.WriteLine(item); } //******************************Output******************************* //Jack //Aimee //******************************************************************* //--------------------------強勢分隔符-------------------------------- //使用SelectMany擴展方法返回我的愛好中有reading的員工的姓名 var selectMany = employees. SelectMany(r => r.Hobby, (r, h) => new { Employee = r, Hobby = h }). Where(r => r.Hobby == "reading"). Select(r => r.Employee.EmployeeName); foreach (var item in selectMany) { Console.WriteLine(item); } //******************************Output******************************* //Jack //Aimee //*******************************************************************

3）排序操做符（OrderBy、ThenBy、OrderByDescending、ThenByDescending、Reverse）

OrderBy、OrderByDescending：升序排序、降序排序

ThenBy、ThenByDescending：若是第一次排序有元素相同，進行第二次排序（使用LINQ查詢時只需把須要排序的關鍵字用逗號隔開）

//按照年齡從大到小排序，若是年齡相同，則按照員工編號正向排序，輸出員工的編號、姓名、年齡,
        var orderBy = from o in employees orderby o.Age descending, o.EmployeeId select o; foreach (var item in orderBy) { Console.WriteLine("EmployeeId: " + item.EmployeeId + " EmployeeName:" + item.EmployeeName + " Age:" + item.Age); } //******************************Output******************************* //EmployeeId: 002 EmployeeName: Jack Age:38 //EmployeeId: 001 EmployeeName: Mike Age:32 //EmployeeId: 006 EmployeeName: Bernie Age:31 //EmployeeId: 010 EmployeeName: Cassie Age:31 //EmployeeId: 004 EmployeeName: Antony Age:30 //EmployeeId: 008 EmployeeName: Duncan Age:30 //EmployeeId: 005 EmployeeName: Asa Age:28 //EmployeeId: 007 EmployeeName: Carl Age:26 //EmployeeId: 003 EmployeeName: Adolph Age:25 //EmployeeId: 009 EmployeeName: Aimee Age:24 //******************************************************************* //--------------------------強勢分隔符-------------------------------- //使用ThenBy擴展方法實現年齡相同，按員工編號正向排序 var thenBy = employees .OrderByDescending(t => t.Age) .ThenBy(t => t.EmployeeId) .Select(t => "EmployeeId: " + t.EmployeeId + " EmployeeName:" + t.EmployeeName + " Age:" + t.Age); foreach (var item in thenBy) { Console.WriteLine(item); } //******************************Output******************************* //EmployeeId: 002 EmployeeName: Jack Age:38 //EmployeeId: 001 EmployeeName: Mike Age:32 //EmployeeId: 006 EmployeeName: Bernie Age:31 //EmployeeId: 010 EmployeeName: Cassie Age:31 //EmployeeId: 004 EmployeeName: Antony Age:30 //EmployeeId: 008 EmployeeName: Duncan Age:30 //EmployeeId: 005 EmployeeName: Asa Age:28 //EmployeeId: 007 EmployeeName: Carl Age:26 //EmployeeId: 003 EmployeeName: Adolph Age:25 //EmployeeId: 009 EmployeeName: Aimee Age:24 //*******************************************************************

Revise：使用擴展方法反轉集合中的元素順序

//按照年齡從大到小排序後再反轉元素的順序
        var reverse = employees .OrderByDescending(r => r.Age) .Reverse() .Select(r => "EmployeeId: " + r.EmployeeId + " EmployeeName:" + r.EmployeeName + " Age:" + r.Age); foreach (var item in reverse) { Console.WriteLine(item); } //******************************Output******************************* //EmployeeId: 009 EmployeeName: Aimee Age:24 //EmployeeId: 003 EmployeeName: Adolph Age:25 //EmployeeId: 007 EmployeeName: Carl Age:26 //EmployeeId: 005 EmployeeName: Asa Age:28 //EmployeeId: 008 EmployeeName: Duncan Age:30 //EmployeeId: 004 EmployeeName: Antony Age:30 //EmployeeId: 010 EmployeeName: Cassie Age:31 //EmployeeId: 006 EmployeeName: Bernie Age:31 //EmployeeId: 001 EmployeeName: Mike Age:32 //EmployeeId: 002 EmployeeName: Jack Age:38 //*******************************************************************

4）鏈接操做符（Join、GroupJoin）

爲了完成這部分的示例，咱們須要準備新的實體類和列表

/// <summary> /// 部門信息 /// </summary> public class DepartmentInfo { //部門編號 public string DepartmentId { get; private set; } //部門名稱 public string DepartmentName { get; private set; } //部門總監 public string Director { get; private set; } public DepartmentInfo(string departmentId, string departmentName, string director) { this.DepartmentId = departmentId; this.DepartmentName = departmentName; this.Director = director; } } /// <summary> /// 傑出團隊 /// </summary> public class OutstandingTeam { public int Year { get; private set; } public string Department { get; private set; } public OutstandingTeam(int year, string department) { this.Year = year; this.Department = department; } }

建立列表departmentInfo保存各部門的信息

List<DepartmentInfo> deparmentInfo = new List<DepartmentInfo>() { new DepartmentInfo("001","HR","Oliver"), new DepartmentInfo("002","IT","Oscar"), new DepartmentInfo("003","PD","ELLA"), new DepartmentInfo("004","FD","Alice"), new DepartmentInfo("005","QC","Kai") };

建立列表outstandingTeams保存2010年起得到傑出團隊的部門

List<OutstandingTeam> outstandingTeams = new List<OutstandingTeam>() { new OutstandingTeam(2010,"IT"), new OutstandingTeam(2011,"FD"), new OutstandingTeam(2012,"HR"), new OutstandingTeam(2013,"IT"), new OutstandingTeam(2014,"QC"), new OutstandingTeam(2015,"HR"), new OutstandingTeam(2016,"HR"), new OutstandingTeam(2017,"MD") };

Join：根據特定的條件合併兩個數據源

//查詢員工的姓名，部門以及該部門的總監
        var join = from j in employees join d in deparmentInfo on j.Department equals d.DepartmentName select new { j.EmployeeName, j.Department, d.Director }; foreach (var item in join) { Console.WriteLine("EmployeeName: " + item.EmployeeName + " Department:" + item.Department + " Director:" + item.Director); } //******************************Output******************************* //EmployeeName: Mike Department:IT Director:Oscar //EmployeeName: Jack Department:HR Director:Oliver //EmployeeName: Adolph Department:IT Director:Oscar //EmployeeName: Antony Department:FD Director:Alice //EmployeeName: Asa Department:FD Director:Alice //EmployeeName: Bernie Department:PD Director:ELLA //EmployeeName: Carl Department:QC Director:Kai //EmployeeName: Aimee Department:HR Director:Oliver //EmployeeName: Cassie Department:IT Director:Oscar //*******************************************************************

這時候咱們會發現，輸出的內容裏面少了員工Duncan的信息，檢查後發現，原來deparmentInfo沒有添加MD部門的相關信息，此時但願查詢全部員工，若匹配不到該部門信息，Director返回N/A。

//查詢員工的姓名，部門以及該部門的總監,若匹配不到該部門信息，Director返回N/A
        var leftjoin = from j in employees join d in deparmentInfo on j.Department equals d.DepartmentName into jd from d in jd.DefaultIfEmpty() select new { j.EmployeeName, j.Department, Director = d == null ? "N/A" : d.Director }; foreach (var item in leftjoin) { Console.WriteLine("EmployeeName: " + item.EmployeeName + " Department:" + item.Department + " Director:" + item.Director); } //******************************Output******************************* //EmployeeName: Mike Department:IT Director:Oscar //EmployeeName: Jack Department:HR Director:Oliver //EmployeeName: Adolph Department:IT Director:Oscar //EmployeeName: Antony Department:FD Director:Alice //EmployeeName: Asa Department:FD Director:Alice //EmployeeName: Bernie Department:PD Director:ELLA //EmployeeName: Carl Department:QC Director:Kai //EmployeeName: Duncan Department:MD Director:N/A //EmployeeName: Aimee Department:HR Director:Oliver //EmployeeName: Cassie Department:IT Director:Oscar //*******************************************************************

GroupJoin：基於鍵相等對兩個序列的元素進行關聯並對結果進行分組。

//查找每一個部門得到傑出團隊的年份
        var groupJoin = from d in deparmentInfo join o in outstandingTeams on d.DepartmentName equals o.Department into g select new { DepartmentName = d.DepartmentName, Years = g }; foreach (var item in groupJoin) { Console.WriteLine("Department:" + item.DepartmentName); if (item.Years.Count() == 0) { Console.WriteLine("Never won the award"); } foreach (var champions in item.Years) { Console.WriteLine(champions.Year); } } //******************************Output******************************* //Department: HR //2012 //2015 //2016 //Department: IT //2010 //2013 //Department: PD // Never won the award // Department:FD //2011 //Department: QC //2014 //*******************************************************************

5）組合操做符（GroupBy、ToLookup）

GroupBy：根據關鍵字值對查詢結果進行分組。

//查詢每一個部門及人數
        var groupBy = from e in employees group e by e.Department into g select new { g.Key, Count = g.Count() }; foreach (var item in groupBy) { Console.WriteLine("Department: " + item.Key + " Count: " + item.Count); } //******************************Output******************************* //Department: IT Count: 3 //Department: HR Count: 2 //Department: FD Count: 2 //Department: PD Count: 1 //Department: QC Count: 1 //Department: MD Count: 1 //*******************************************************************

ToLookup：經過建立一對多的字典來組合元素

//使用ToLookup實現愛好閱讀的員工姓名
        var toLookup = (from e in employees from h in e.Hobby select new { Hobby = h, Name = e.EmployeeName }).ToLookup(he => he.Hobby, he => he.Name); if (toLookup.Contains("reading")) { foreach (var item in toLookup["reading"]) { Console.WriteLine(item); } } //******************************Output******************************* //Jack //Aimee //*******************************************************************

6）限定操做符（Any、All、Contains）

Any：是否包含知足條件的元素

//是否有小於20歲的員工
        bool any = employees.Any(r => r.Age < 20); Console.WriteLine(any); //******************************Output******************************* //False //*******************************************************************

ALL：是否全部元素都知足條件

//是否全部員工都大於20歲
        bool all = employees.All(r => r.Age > 20); Console.WriteLine(all); //******************************Output******************************* //True //*******************************************************************

Contains：檢索某個元素是否在集合中

//員工列表中是否包含david
        Employee david = new Employee("011", "David", 28, new DateTime(2017, 5, 21), Sex.Male, Department.IT, 100000, new string[] { "run" }); employees.Add(david); bool contains = employees.Contains(david); Console.WriteLine(contains); //******************************Output******************************* //True //*******************************************************************

7）分區操做符（Take、Skip、TakeWhile、SkipWhile）

Take：從集合中提取指定數量的元素

Skip：跳過集合中指定數量的元素

//忽略薪水最高的5位，查詢剩餘部分薪水最高的員工姓名及薪水
        var skip = (from e in employees orderby e.Salary descending select e).Skip(5).Take(1); foreach (var item in skip) { Console.WriteLine("EmployeeName: " + item.EmployeeName + " Salary: " + item.Salary); } //******************************Output******************************* //EmployeeName: Mike Salary: 200000 //*******************************************************************

TakeWhile：提取條件爲真時的元素

//取集合中知足條件salary大於1000000以前的全部員工的姓名和薪水
        var takeWhile = (from e in employees select e).TakeWhile(r => r.Salary > 100000); foreach (var item in takeWhile) { Console.WriteLine("EmployeeName: " + item.EmployeeName + " Salary: " + item.Salary); } //******************************Output******************************* //EmployeeName: Mike Salary: 200000 //EmployeeName: Jack Salary: 409989 //*******************************************************************

SkipWhere：跳過集合中知足條件的元素，當條件不成立時返回剩餘的全部元素

//跳過集合中知足條件salary大於100000的元素，當條件不成立時返回剩餘的全部元素
        var skipWhile = (from e in employees select e).SkipWhile(r => r.Salary > 100000); foreach (var item in skipWhile) { Console.WriteLine("EmployeeName: " + item.EmployeeName + " Salary: " + item.Salary); } //******************************Output******************************* //EmployeeName: Adolph Salary: 100000 //EmployeeName: Antony Salary: 320000 //EmployeeName: Asa Salary: 120000 //EmployeeName: Bernie Salary: 220000 //EmployeeName: Carl Salary: 100000 //EmployeeName: Duncan Salary: 250000 //EmployeeName: Aimee Salary: 80000 //EmployeeName: Cassie Salary: 350000 //*******************************************************************

8）Set操做符（Distinct、Union、Intersect、Except、Zip）

Distinct：從集合中刪掉重複的元素

//給全部員工的薪水排序，去掉重複的
        var distinct = (from e in employees orderby e.Salary select e.Salary).Distinct(); foreach (var item in distinct) { Console.WriteLine(item); } //******************************Output******************************* //80000 //100000 //120000 //200000 //220000 //250000 //320000 //350000 //409989 //*******************************************************************

Union、Intersect、Except：並集、交集、差集

首先，咱們準備兩個集合：員工姓名以A開頭和員工姓名以E結尾

var startWithA = (from e in employees where e.EmployeeName.StartsWith("A") select e).ToList(); var endWithE = (from e in employees where e.EmployeeName.ToUpper().EndsWith("E") select e).ToList();

如下分別取兩個集合的並集、交集、差集：

//查詢兩個集合的並集
        var union = startWithA.Union(endWithE); foreach (var item in union) { Console.WriteLine(item.EmployeeName); } //******************************Output******************************* //Adolph //Antony //Asa //Aimee //Mike //Bernie //Cassie //******************************************************************* //--------------------------強勢分隔符-------------------------------- //查詢兩個集合的交集 var intersect = startWithA.Intersect(endWithE); foreach (var item in intersect) { Console.WriteLine(item.EmployeeName); } //******************************Output******************************* //Aimee //******************************************************************* //--------------------------強勢分隔符-------------------------------- //查詢兩個集合的差集 var except = startWithA.Except(endWithE); foreach (var item in except) { Console.WriteLine(item.EmployeeName); } //******************************Output******************************* //Adolph //Antony //Asa //*******************************************************************

Zip：把兩個集合中對應的項目合併起來，在到大較小集合的末尾時中止

//把兩個集合中對應的項的姓名合併起來
        var zip = startWithA.Zip(endWithE, (first, second) => first.EmployeeName + "+" + second.EmployeeName); foreach (var item in zip) { Console.WriteLine(item); } //******************************Output******************************* //Adolph+Mike //Antony+Bernie //Asa+Aimee //Aimee+Cassie //*******************************************************************

9）元素操做符（First、FirstOrDefault、Last、LastOrDefault、ElementAt、ElementAtOrDefault、Single、SingleOrDefault）

First：返回第一個知足條件的元素；若不存在，則引起異常。

FirstOrDefault：返回第一個知足條件的元素；若不存在，則返回默認值。

//查詢年齡大於30歲的第一位員工的姓名
        var first = (from e in employees orderby e.Age select e).First(r => r.Age > 30); Console.WriteLine(first.EmployeeName); //******************************Output******************************* //Bernie //*******************************************************************

假設需查詢年齡大於50歲的第一位員工的姓名，咱們將上述代碼中年齡修改成50

var first = (from e in employees orderby e.Age select e).First(r => r.Age > 50); Console.WriteLine(first.EmployeeName);

執行後發現異常

此時使用FirstOrDefault操做符：

//查詢年齡大於50歲的第一位員工的姓名,若不存在，則返回N/A
        var firstOrDefault = (from e in employees orderby e.Age select e).FirstOrDefault(r => r.Age > 50); Console.WriteLine(firstOrDefault == null ? "N/A" : firstOrDefault.EmployeeName); //******************************Output******************************* //N/A //*******************************************************************

Last：返回最後一個知足條件的元素；若不存在，則引起異常。

LastOrDefault：返回最後一個知足條件的元素；若不存在，則返回默認值。

ElementAt：返回指定索引位置的元素；若不存在，則引起異常。

ElementAtOrDefault：返回指定索引位置的元素；若不存在，則返回默認值。

Single：只返回一個知足條件的元素；若不存在或多個元素都知足條件，則引起異常。

SingleOrDefault：只返回一個知足條件的元素；若不存在或多個元素都知足條件，則返回默認值。

10）聚合操做符（Count、Sum、Min、Max、Average、Aggregate）

Count：返回集合中的項數

//查找有一個以上愛好的員工的姓名、愛好的數量及部門
        var count = from e in employees let numberHobby = e.Hobby.Count() where numberHobby > 1 select new { e.EmployeeName, numberHobby, e.Department }; foreach (var item in count) { Console.WriteLine("EmployeeName: " + item.EmployeeName + " NumberHobby: " + item.numberHobby + " Department: " + item.Department); } //******************************Output******************************* //EmployeeName: Mike NumberHobby: 2 Department: IT //EmployeeName: Adolph NumberHobby: 3 Department: IT //EmployeeName: Antony NumberHobby: 2 Department: FD //EmployeeName: Carl NumberHobby: 2 Department: QC //EmployeeName: Aimee NumberHobby: 2 Department: HR //*******************************************************************

Sum：計算全部值的總和

Min、Max、Average：最小值、最大值、平均值

//計算全部員工薪水的總和
        var sum = (from e in employees select e.Salary).Sum/*Min、Max、Average*/(); Console.WriteLine(sum.ToString("N0")); //******************************Output******************************* //2,149,989 //*******************************************************************

Aggregate：對序列進行累加

//初始值爲50000000，依次累加全部員工的薪水
        var aggregate = (from e in employees select e.Salary).Aggregate(5000000, (x, y) => x + y, r => r * 2); Console.WriteLine(aggregate.ToString("N0")); //******************************Output******************************* //14,299,978 //*******************************************************************

說明：Aggregate擴展方法的第一個參數爲初始值。第二個參數是一個表達式，用來對每一個元素進行計算（第一個參數是累加變量，第二個參數是當前值）。第三個參數是一個表達式，用來對最終結果進行計算。

11）轉換操做符（ToArray、AsEnumerable、ToList、ToDictionary、Cast<TResult>）

使用轉換操做符會當即執行查詢，將查詢結果放在數組、列表、字典中。

//將年齡大於30歲的元素放入list中再循環輸出。
        List<Employee> employeeList = (from e in employees where e.Age > 30 select e).ToList(); foreach (var item in employeeList) { Console.WriteLine("EmployeeName: " + item.EmployeeName + " Age:" + item.Age); } //******************************Output******************************* //EmployeeName: Mike Age:32 //EmployeeName: Jack Age:38 //EmployeeName: Bernie Age:31 //EmployeeName: Cassie Age:31 //*******************************************************************

12）生成操做符（Empty、Range、Repeat）

生成操做符不是擴展方法，而是返回序列的靜態方法。在LINQ to Objects中，這些方法可用於Enumerable類。

Empty：生成空集合

//生成一個int類型的空序列
        var empty = Enumerable.Empty<int>(); Console.WriteLine(empty.Count()); //******************************Output******************************* //0 //*******************************************************************

Range：生成一系列數字的集合

//生成一個從1開始，10個元素的序列
        var range = Enumerable.Range(1, 10); foreach (var item in range) { Console.WriteLine(item); } //******************************Output******************************* //1 //2 //3 //4 //5 //6 //7 //8 //9 //10 //*******************************************************************

Repeat：返回始終重複一個值的集合

//生成一個10個元素，每一個元素都是5的序列
        var repeat = Enumerable.Repeat(5, 10); foreach (var item in repeat) { Console.WriteLine(item); } //******************************Output******************************* //5 //5 //5 //5 //5 //5 //5 //5 //5 //5 //*******************************************************************

本篇就此結束，主要介紹了LINQ的體系結構、基本語法以及LINQ to Obejcts中標準查詢操做符的使用方法。

示例代碼下載： https://github.com/Answer-Geng/LINQ