using System; using System.Collections.Generic; using System.Linq; class LinqDemo { static void Main() { string[] names = { "Tom", "Dick", "Harry" }; IEnumerable<string> filteredNames = names.Where(n => n.Length >= 4); foreach (string name in filteredNames) Console.Write(name + "|"); } }
LINQ
Assign the loop variable to another variable declared inside the statement block
using System; using System.Collections.Generic; using System.Linq; public class MainClass { public static void Main() { IEnumerable<char> vowels = "aeiou"; IEnumerator<char> rator = vowels.GetEnumerator(); IEnumerable<char> query = "Not what you might expect"; foreach (char vowel in "aeiou") { char temp = vowel; query = query.Where(c => c != temp); } } }
use where clause in a while loop
using System; using System.Collections.Generic; using System.Linq; public class MainClass { public static void Main() { IEnumerable<char> vowels = "aeiou"; IEnumerator<char> rator = vowels.GetEnumerator(); IEnumerable<char> query = "Not what you might expect"; char vowel; while (rator.MoveNext()) { vowel = rator.Current; query = query.Where(c => c != vowel); } } }
Two where clauses
using System; using System.Collections; using System.Collections.Generic; using System.Text; using System.Linq; class Employee { int _id; int _idRole; string _lastName; string _firstName; public int ID { get { return _id; } set { _id = value; } } public int IDRole { get { return _idRole; } set { _idRole = value; } } public string LastName { get { return _lastName; } set { _lastName = value; } } public string FirstName { get { return _firstName; } set { _firstName = value; } } } class Salary { int _id; int _year; double _salary; public int ID { get { return _id; } set { _id = value; } } public int Year { get { return _year; } set { _year = value; } } public double SalaryPaid { get { return _salary; } set { _salary = value; } } } public class MainClass { public static void Main() { List<Employee> people = new List<Employee> { new Employee { ID = 1, IDRole = 1, LastName = "A", FirstName = "B"}, new Employee { ID = 2, IDRole = 2, LastName = "G", FirstName = "T"} }; List<Salary> salaries = new List<Salary> { new Salary { ID = 1, Year = 2004, SalaryPaid = 10000.00 }, new Salary { ID = 1, Year = 2005, SalaryPaid = 15000.00 }, new Salary { ID = 1, Year = 2005, SalaryPaid = 15000.00 } }; IEnumerable<Salary> q = from p in people where p.ID == 1 from s in salaries where s.ID == p.ID select s; } }
prints strings where each element has the second letter 'i'.
using System; using System.Collections.Generic; using System.Linq; using System.Text; public class MainClass { public static void Main() { string[] digits = { "ziro", "one", "two", "three"}; var reversedIDigits = ( from d in digits where d[1] == 'i' select d) .Reverse(); foreach (var d in reversedIDigits) { Console.WriteLine(d); } } }
Filtered: prints the name of each element of an integer array that is less than 5
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
public class MainClass {
public static void Main() {
int[] numbers = { 5, 4, 1, 3};
string[] digits = { “zero”, “one”, “two”, “three”};
var lowNums =
from n in numbers
where n < 5
select digits[n];
Console.WriteLine("Numbers < 5:");
foreach (var num in lowNums) {
Console.WriteLine(num);
}
}
}
[/csharp]
Use && in where clause
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
public class MainClass {
public static void Main() {
List
var expensiveInStockProducts =
from p in products
where p.UnitsInStock > 0 && p.UnitPrice > 3.00M
select p;
foreach (var product in expensiveInStockProducts) {
Console.WriteLine(product.ProductName);
}
}
static List
List
empTree.Add(new Product { ProductName = “A”, Category = “O”, UnitPrice = 12, UnitsInStock = 5, Total = 36, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = “B”, Category = “O”, UnitPrice = 2, UnitsInStock = 4, Total = 35, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = “C”, Category = “O”, UnitPrice = 112, UnitsInStock = 3, Total = 34, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = “D”, Category = “O”, UnitPrice = 112, UnitsInStock = 0, Total = 33, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = “E”, Category = “O”, UnitPrice = 1112, UnitsInStock = 2, Total = 32, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
empTree.Add(new Product { ProductName = “F”, Category = “O”, UnitPrice = 11112, UnitsInStock = 0, Total = 31, OrderDate = new DateTime(2005, 1, 1), Id = 1 });
return empTree;
}
}
class Product : IComparable
public string ProductName { get; set; }
public string Category { get; set; }
public int UnitPrice { get; set; }
public int UnitsInStock { get; set; }
public int Total { get; set; }
public DateTime OrderDate { get; set; }
public int Id { get; set; }
public override string ToString() {
return String.Format(“Id: {0}, Name: {1} , Category: {3}”, this.Id, this.ProductName, this.Category);
}
int IComparable
if (other == null)
return 1;
if (this.Id > other.Id)
return 1;
if (this.Id < other.Id) return -1; return 0; } } [/csharp]