using System; using System.Collections; using System.Collections.Generic; using System.Linq; static class Samples { static int[] numbers = new [] { 5, 4, 1, 3, 9, 8, 6, 7, 2, 0 }; static string[] strings = new [] { "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine" }; class Person { public string Name {get; set;} public int Level {get; set;} } static Person[] persons = new Person[] { new Person {Name="Jesper", Level=3}, new Person {Name="Lene", Level=3}, new Person {Name="Jonathan", Level=5}, new Person {Name="Sagiv", Level=3}, new Person {Name="Jacqueline", Level=3}, new Person {Name="Ellen", Level=3}, new Person {Name="Gustavo", Level=9} }; public static void Sample1() { // use Where() to filter out elements matching a particular condition var fnums = numbers.Where(n => n < 5); Console.WriteLine("Numbers < 5"); foreach(int x in fnums) { Console.WriteLine(x); } } 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); } public static void Sample3() { // use Select() to convert each element into a new value var snums = numbers.Select(n => strings[n]); Console.WriteLine("Numbers"); foreach(string s in snums) { Console.WriteLine(s); } } 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); } } 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); } } 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); } } 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 string foreach(var g in q) { Console.WriteLine("Group: {0}", g.Key); foreach(string v in g) { Console.WriteLine("\tValue: {0}", v); } } } 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); } } public static void Sample9() { // use OrderBy()/OrderByDescending() to give order to your resulting sequence var q = strings.OrderBy(s => s); // order the strings by their name foreach(string s in q) { Console.WriteLine(s); } } 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); } } public static void Sample10() { // use query expressions to simplify var q = from p in persons orderby p.Level, p.Name group p.Name by p.Level into g select new {Level = g.Key, Persons = g}; foreach(var g in q) { Console.WriteLine("Level: {0}", g.Level); foreach(var p in g.Persons) { Console.WriteLine("Person: {0}", p); } } } }
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