Linq 入门系列 select篇
其实也是对网上linq--select篇的扩充
我在这里把两种语法都写,lambda,linq写法，方便大家更好的去学习，同时也增加了一些新的东西，如解释，例子的扩充。。。
今后一段时间，我会对linq一些基本写法进行例子和解释结合的方式和大家进行分享。
class Program
{
private static List<Student> GetStudents()
{
List<Student> students = new List<Student> { new Student{ Name="YOUNG", Age=25, Language="Chinese"}, new Student{ Name="JESSIE", Age=21, Language="Scotland"}, new Student{ Name="KELLY", Age=18, Language="English"}, new Student{ Name="JUNE", Age=20, Language="English"}, new Student{ Name="ADRIAN", Age=22, Language="Italy"}, new Student{ Name="BRUCE", Age=17, Language="Scotland"}, new Student{ Name="BRANT", Age=30, Language="Germany"}, new Student{ Name="BEN", Age=25, Language="Chinese"}
}; return students; } static void Main(string[] args) { List<Student> studentList = GetStudents(); Select(studentList); } private static void Select<T>(T studentList) { OnlySearch(studentList); SearchCollectChangeOtherCollect(studentList); BuilderAnomy(); BuilderAnomyExter(); SelectLambda(); ComplexSelect(); ComplexSelectLambda(); } private static void OnlySearch<T>(T studentList) { Console.WriteLine("<hr>只查询合适对象集合的某个属性：<br>"); //lamb的写法 var students = RevealChangeType(studentList).Where(n=>n.Language == "Chinese").Select(n=>n.Name); //linq的写法 //var students = from n in RevealChangeType(studentList) // where n.Language == "Chinese" // select n.Name; foreach (var student in students) { Console.WriteLine(string.Format("<span class='result'>{0}</span>", student)); } } private static IEnumerable<Student> RevealChangeType<T>(T obj) { IEnumerable<Student> student = obj as IEnumerable<Student>; return student; } private static void SearchCollectChangeOtherCollect<T>(T obj) { Console.WriteLine("<hr>从一个集合中查询，转化到另外一个集合：<br>"); //age Array int[] intArray ={ 25, 1, 4, 3 }; //lamb的写法 var students = intArray.SelectMany(n=>RevealChangeType(obj).Where(s=>s.Age == n)); //linq的写法 //var students = from s in RevealChangeType(obj) // from n in intArray // where s.Age == n // select s; foreach (var student in students) { Console.WriteLine(string.Format("<span class='result'>{0}</span>", student.Name)); } } private static void BuilderAnomy() { Console.WriteLine("<hr>构建匿名类型：<br>"); List<Student> studentList = GetStudents(); int[] intArray = { 3, 1, 6, 4 }; //lamb的写法 var stu = intArray.Select(n=>new { Id = n, Name = (studentList as List<Student>)[n].Name }); //linq的写法 //var stu = from n in intArray // select new{Id = n,Name=(studentList as List<Student>)[n].Name}; foreach (var s in stu) { Console.WriteLine(string.Format("<div class='result'>id:{0};name:{1}</div>", s.Id, s.Name)); } } private static void BuilderAnomyExter() { Console.WriteLine("<hr>构建匿名类型2——扩展已有类：<br>"); List<Student> studentList = GetStudents(); int[] intArray = { 3, 1, 6, 4 }; //lamb的写法 var students = intArray.Select(n=>new { Id = n, studentList[n].Name, studentList[n].Age }); //linq的写法 //var students = from n in intArray // select new {Id = n, studentList[n].Name, studentList[n].Age}; foreach (var student in students) { Console.WriteLine(string.Format("<div class='result'>id:{0}; name:{1}; age:{2}</div>", student.Id, student.Name, student.Age)); } } private static void SelectLambda() { Console.WriteLine("<hr>select的Lambda表达式：<br>"); List<Student> studentList = GetStudents(); int[] intArray = { 3, 1, 6, 4 }; //lamb的写法 var stu = intArray.Select(i=>new { Id = i, studentList[i].Name }); //linq的写法 //var stu = from i in intArray // select new {Id = i, studentList[i].Name}; foreach (var student in stu) { Console.WriteLine(string.Format("<div class='result'>id:{0}; name:{1}</div>", student.Id, student.Name)); } } private static void ComplexSelect() { Console.WriteLine("<hr>复合选择：<br>"); List<Student> studentList = GetStudents(); string[] stringArray = { "Ajax", "Csharp", "Javascript", "Css Desige", "Asp.net", "Gis" }; //lamb的写法 //var stu = stringArray.Where(s=>s.Length > 8).SelectMany(s=>studentList.Where(str1=>str1.Age > 23).Select(str=>new { book = s, name = str.Name })); var stu = studentList.Where(sl=>sl.Age > 23).SelectMany(sl=>stringArray.Where(s=>s.Length > 8).Select(s=>new { name = sl.Name, book = s })); //linq的写法 //var stu = from sl in studentList // where sl.Age > 23 // from s in stringArray // where s.Length > 8 // select new {name = sl.Name, book = s}; foreach (var student in stu) { Console.WriteLine(string.Format("<div class='result'>{0} is studying {1}</div>", student.name, student.book)); } } private static void ComplexSelectLambda() { Console.WriteLine("<hr>多重选择的Lambda表达式：<br>"); List<Student> studentList = GetStudents(); string[] stringArray = { "Ajax", "Csharp", "Javascript", "Css Desige", "Asp.net", "Gis" }; //lamb的写法 //var stu = studentList.SelectMany(s=>stringArray.Select(str => s.Name + "has a book names " + str)); //linq的写法 var stu = from sl in studentList from s in stringArray select new {name=sl.Name,language=s}; foreach (var s in stu) { Console.WriteLine(string.Format("<div class='result'>{0}</div>", s)); } }
} sealed class Student { public int age; public int Age { get { return age; } set { age = value; } } private string name; public string Name { get { return name; } set { name = value; } } private string language; public string Language { get { return language; } set { language = value; } } }对此方法的补充 ComplexSelectLambda()**********************************但是现在（ComplexSelectLambda()）输出的结果是：<hr>多重选择的Lambda表达式：<br/><div class='result'>{name=YOUNG, language=Ajax}</div><div class='result'>{name=YOUNG, language=Csharp}</div><div class='result'>{name=YOUNG, language=Javascript}</div><div class='result'>{name=YOUNG, language=Css Desige}</div><div class='result'>{name=YOUNG, language=Asp.net}</div><div class='result'>{name=YOUNG, language=Gis}</div>**********************************//////////////////////////////////问题：如何写才能输入这样的结果？ <name=young,language=Ajax><name=JESSIE,language=Csharp><name=KELLY,language=Javascript><name=JUNE,language=Css Desige><name=ADRIAN,language=Asp.net><name=BRUCE,language=Gis>//////////////////////////////////代码：private static void ComplexSelectLambdaTwo() { Console.WriteLine("<hr>多重选择的Lambda表达式：<br>"); List<Student> studentList = GetStudents(); string[] stringArray = { "Ajax", "Csharp", "Javascript", "Css Desige", "Asp.net", "Gis" }; var langlist = stringArray.Select(( la, i) => new { lang = la, index = i }); var stulist = studentList.Select(( st, i) => new { name = st.Name, index = i }); var stu2 = from la in langlist from st in stulist where la.index == st.index select new {name = st.name, language = la.lang}; foreach (var s2 in stu2) { Console.WriteLine(string.Format("<name={0},language={1}>", s2.name, s2.language)); } }
