Lambda表达式练习

根据微软的示例代码,体验一下

1.准备测试数据static int[] numbers = new int[] { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 };static string[] strings = new string[] { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine"};class Person {public string Name;public int Level;}static Person[] persons = new Person[] {new Person {Name="Matt", Level=3},new Person {Name="Luca", Level=3},new Person {Name="Jomo", Level=5},new Person {Name="Dinesh", Level=3},new Person {Name="Charlie", Level=3},new Person {Name="Mads", Level=3},new Person {Name="Anders", Level=9}};2.过滤数据public static void Sample1() {// use Where() to filter out elements matching a particular condition               IEnumerable<int> fnums = numbers.Where(n => n < 5);Console.WriteLine("Numbers < 5");foreach(int x in fnums) {Console.WriteLine(x);}}3.匹配首个字母public static void Sample2() {// use First() to find the one element matching a particular condition               string v = strings.First(s => s[0] == 'o');Console.WriteLine("string starting with 'o': {0}", v);}4.根据numbers排序public static void Sample3() {// use Select() to convert each element into a new value        IEnumerable<string> snums = numbers.Select(n => strings[n]);Console.WriteLine("Numbers");foreach(string s in snums) {Console.WriteLine(s);}}5.匿名类型,注意var关键字public static void Sample4(){// use Anonymous Type constructors to construct multi-valued results on the fly        var q = strings.Select(s => new {Head = s.Substring(0,1), Tail = s.Substring(1)});foreach(var p in q) {Console.WriteLine("Head = {0}, Tail = {1}", p.Head, p.Tail);}}6.联合查询(即使用两个以上的查询条件)public static void Sample5() {// Combine Select() and Where() to make a complete query        var q = numbers.Where(n => n < 5).Select(n => strings[n]);Console.WriteLine("Numbers < 5");foreach(var x in q) {Console.WriteLine(x);}}7.使用ToList方法缓存数据,不知道这样说对不对public static void Sample6() {// Sequence operators form first-class queries are not executed until you enumerate them.        int i = 0;var q = numbers.Select(n => ++i);// Note, the local variable 'i' is not incremented until each element is evaluated (as a side-effect).        foreach(var v in q) {Console.WriteLine("v = {0}, i = {1}", v, i);}Console.WriteLine();// Methods like ToList() cause the query to be executed immediately, caching the results        int i2 = 0;var q2 = numbers.Select(n => ++i2).ToList();// The local variable i2 has already been fully incremented before we iterate the results        foreach(var v in q2) {Console.WriteLine("v = {0}, i2 = {1}", v, i2);}}8.分组查询public static void Sample7() {// use GroupBy() to construct group partitions out of similar elements        var q = strings.GroupBy(s => s[0]); // <- group by first character of each stringforeach(var g in q) {Console.WriteLine("Group: {0}", g.Key);foreach(string v in g) {Console.WriteLine("/tValue: {0}", v);}}}9.统计聚合public static void Sample8() {// use GroupBy() and aggregates such as Count(), Min(), Max(), Sum(), Average() to compute values over a partition        var q = strings.GroupBy(s => s[0]).Select(g => new {FirstChar = g.Key, Count = g.Count()});foreach(var v in q) {Console.WriteLine("There are {0} string(s) starting with the letter {1}", v.Count, v.FirstChar);}}10.排序// use OrderBy()/OrderByDescending() to give order to your resulting sequence        var q = strings.OrderBy(s => s);  // order the strings by their nameforeach(string s in q) {Console.WriteLine(s);}}11.二次排序public static void Sample9a() {// use ThenBy()/ThenByDescending() to provide additional ordering detail        var q = persons.OrderBy(p => p.Level).ThenBy(p => p.Name);foreach(var p in q) {Console.WriteLine("{0}  {1}", p.Level, p.Name);}}