Csharp/CSharp Tutorial/LINQ/select

Converting an Array of Strings to Integers

using System;
using System.Linq;
public class MainClass {
    public static void Main() {
        string[] numbers = { "0042", "010", "9", "2q7" };
        int[] nums = numbers.Select(s => Int32.Parse(s)).ToArray();
    }
}

Converting an Array of Strings to Integers and Sorting It

using System;
using System.Linq;
public class MainClass {
    public static void Main() {
        string[] numbers = { "0042", "010", "9", "2q7" };
        int[] nums = numbers.Select(s => Int32.Parse(s)).OrderBy(s => s).ToArray();
        foreach (int num in nums)
            Console.WriteLine(num);
    }
}

Delegate targets

using System;
using System.Collections.Generic;
using System.Text;
using System.Linq;
    class MainClass
    {
        public static void Main()
        {
            string[] currentVideoGames = {"Shooting", "D","Half Life", "F.E.A.R.","Game", "System"};
            Func<string, bool> searchFilter = new Func<string, bool>(Filter);
            Func<string, string> itemToProcess = new Func<string,string>(ProcessItem);
            var subset = currentVideoGames.Where(searchFilter).OrderBy(itemToProcess).Select(itemToProcess);
            foreach (var game in subset)
                Console.WriteLine("Item: {0}", game);
        }
        public static bool Filter(string s) {return s.Length > 6;}
        public static string ProcessItem(string s) { return s; }
    }

Demonstrating the Query Results Changing Between Enumerations

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
public class MainClass {
    public static void Main() {
        int[] intArray = new int[] { 1, 2, 3 };
        IEnumerable<int> ints = intArray.Select(i => i);
        foreach (int i in ints)
            Console.WriteLine(i);
        intArray[0] = 5;
        foreach (int i in ints)
            Console.WriteLine(i);
    }
}

Query Reuse

using System;
using System.Linq;
static class QueryReuse {
    static double Square(double n) {
        Console.WriteLine("Computing Square(" + n + ")...");
        return Math.Pow(n, 2);
    }
    public static void Main() {
        int[] numbers = { 1, 2, 3 };
        var query =
          from n in numbers
          select Square(n);
        foreach (var n in query)
            Console.WriteLine(n);
        for (int i = 0; i < numbers.Length; i++)
            numbers[i] = numbers[i] + 10;
        foreach (var n in query)
            Console.WriteLine(n);
    }
}

Query with Intentional Exception Deferred Until Enumeration

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
public class MainClass {
    public static void Main() {
        string[] strings = { "one", "two", null, "three" };
        Console.WriteLine("Before Where() is called.");
        IEnumerable<string> ieStrings = strings.Where(s => s.Length == 3);
        Console.WriteLine("After Where() is called.");
        foreach (string s in ieStrings) {
            Console.WriteLine("Processing " + s);
        }
    }
}

Returning a List

using System;
using System.Linq;
using System.Collections;
using System.Collections.Generic;
public class MainClass {
    public static void Main() {
        int[] intArray = new int[] { 1, 2, 3 };
        List<int> ints = intArray.Select(i => i).ToList();
        foreach (int i in ints)
            Console.WriteLine(i);
        intArray[0] = 5;
        foreach (int i in ints)
            Console.WriteLine(i);
    }
}

Select all from a List

using System;
using System.Collections.Generic;
using System.Text;
using System.Xml.Linq;
using System.Linq;
class Car
{
    public string PetName;
    public string Color;
    public int Speed;
    public string Make;
    public override string ToString()
    {
        return string.Format("Make={0}, Color={1}, Speed={2}, PetName={3}", Make, Color, Speed, PetName);
    }
}
class Program
{
    static void Main(string[] args)
    {
        Car[] myCars = new[]{
                new Car{ PetName = "A", Color = "Silver", Speed = 100, Make = "BMW"},
                new Car{ PetName = "B", Color = "Black", Speed = 55, Make = "VW"},
                new Car{ PetName = "C", Color = "White", Speed = 43, Make = "Ford"}
            };

        var subset = from c in myCars select c;
        foreach (var c in subset)
        {
            Console.WriteLine(c.ToString());
        }

    }
}

Select array item by type

using System;
using System.Linq;
static class TestArray {
    static void Main() {
        Object[] array = { "String", 12, true, "a" };
        var types =
          array
            .Select(item => item.GetType().Name)
            .OrderBy(type => type);
    }
}

Select Distinct

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
    class Customer
    {
        public string ID { get; set; }
        public string City { get; set; }
        public string Country { get; set; }
        public string Region { get; set; }
        public decimal Sales { get; set; }
        public override string ToString()
        {
            return "ID: " + ID + " City: " + City + " Country: " + Country + " Region: " + Region + " Sales: " + Sales;
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            List<Customer> customers = new List<Customer> {
              new Customer { ID="Q", City="London", Country="UK", Region="Europe", Sales=8000 },
              new Customer { ID="R", City="Beijing", Country="China", Region="Asia", Sales=9000 },
              new Customer { ID="T", City="Lima", Country="Peru", Region="South America", Sales=2002 }
           };
            var queryResults = customers.Select(c => c.Region).Distinct();
            foreach (var item in queryResults)
            {
                Console.WriteLine(item);
            }
        }
    }

Select only pet name

using System;
using System.Collections.Generic;
using System.Text;
using System.Xml.Linq;
using System.Linq;
    class Car
    {
        public string PetName;
        public string Color;
        public int Speed;
        public string Make;
        
        public override string ToString()
        {
            return string.Format("Make={0}, Color={1}, Speed={2}, PetName={3}",Make, Color, Speed, PetName);
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            Car[] myCars = new []{
                new Car{ PetName = "A", Color = "Silver", Speed = 100, Make = "BMW"},
                new Car{ PetName = "B", Color = "Black", Speed = 55, Make = "VW"},
                new Car{ PetName = "C", Color = "White", Speed = 43, Make = "Ford"}
            };
        
            var names = from c in myCars select c.PetName;
            foreach (var n in names)
            {
                Console.WriteLine("Name: {0}", n);
            }
        
        
        }
    }

Select sum value

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
    class Employee
    {
        public string Name { get; set; }
        public decimal Salary { get; set; }
    }
    class Department
    {
        public string Name { get; set; }
        List<Employee> employees = new List<Employee>();
        public IList<Employee> Employees
        {
            get { return employees; }
        }
    }
    class Company
    {
        public string Name { get; set; }
        List<Department> departments = new List<Department>();
        public IList<Department> Departments
        {
            get { return departments; }
        }
    }
    class SalaryReport
    {
        static void Main()
        {
            var company = new Company
            {
                Name = "A",
                Departments =
                {
                    new Department 
                    { 
                        Name = "Development", 
                        Employees = 
                        {
                            new Employee { Name = "T", Salary = 75000m },
                            new Employee { Name = "D", Salary = 45000m },
                            new Employee { Name = "M", Salary = 150000m }
                        }
                    },
                    new Department 
                    { 
                        Name = "Marketing", 
                        Employees = 
                        {
                            new Employee { Name = "Z", Salary = 200000m },
                            new Employee { Name = "X", Salary = 120000m }
                        }
                    }
                }
            };
            var query = company.Departments
                               .Select(dept => new { dept.Name, Cost = dept.Employees.Sum(person => person.Salary) })
                               .OrderByDescending(deptWithCost => deptWithCost.Cost);
            foreach (var item in query)
            {
                Console.WriteLine(item);
            }
        }
    }

Select with Anonymous Types: iterates over each element to print the element"s name

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
public class MainClass {
    public static void Main() {
        int[] numbers = { 5, 4, 1};
        string[] strings = { "zero", "one", "two"};
        var digitOddEvens =
            from n in numbers
            select new { Digit = strings[n], Even = (n % 2 == 0) };
        foreach (var d in digitOddEvens) {
            Console.WriteLine("The digit {0} is {1}.", d.Digit, d.Even ? "even" : "odd");
        }
    }
}

Select with Anonymous Types: prints the name of every product in the product list along with the category of the product and its unit price

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
public class MainClass {
    public static void Main() {
        List<Product> products = GetProductList();
        var productInfos =
            from p in products
            select new { p.ProductName, p.Category, Price = p.UnitPrice };
        Console.WriteLine("Product Info:");
        foreach (var productInfo in productInfos) {
            Console.WriteLine("{0} is in the category {1} and costs {2} per unit.", productInfo.ProductName, productInfo.Category, productInfo.Price);
        }
    }
    static List<Product> GetProductList() {
        List<Product> empTree = new List<Product>();
        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<Product> {
    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<Product>.rupareTo(Product other) {
        if (other == null)
            return 1;
        if (this.Id > other.Id)
            return 1;
        if (this.Id < other.Id)
            return -1;
        return 0;
    }
}

Select with Anonymous Types: prints uppercase and lowercase versions of each string in an input array

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
public class MainClass {
    public static void Main() {
        string[] words = { "Abc", "aBc", "AAA" };
        var upperLowerWords =
            from w in words
            select new { Upper = w.ToUpper(), Lower = w.ToLower() };
        foreach (var ul in upperLowerWords) {
            Console.WriteLine("Uppercase: {0}, Lowercase: {1}", ul.Upper, ul.Lower);
        }
    }
}

Transformation: link two array.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
public class MainClass {
    public static void Main() {
        int[] numbers = { 5, 4, 1};
        string[] strings = { "zero", "one", "two"};
        var textNums =
            from n in numbers
            select strings[n];
        Console.WriteLine("Number strings:");
        foreach (var s in textNums) {
            Console.WriteLine(s);
        }
    }
}

Use LINQ to query characters in a string

using System;
using System.Collections.Generic;
using System.Linq;
static class TestString {
    static void Main() {
        var count =
          "abc 8"
          .Where(c => !Char.IsLetter(c))
          .Count();
        Console.WriteLine(count);
    }
}

Use LINQ with Dictionary

using System;
using System.Collections.Generic;
using System.Linq;
static class TestDictionary {
    static void Main() {
        Dictionary<int, string> frenchNumbers;
        frenchNumbers = new Dictionary<int, string>();
        frenchNumbers.Add(0, "zero");
        frenchNumbers.Add(1, "one");
        frenchNumbers.Add(2, "two");
        frenchNumbers.Add(3, "three");
        frenchNumbers.Add(4, "four");
        var evenFrenchNumbers =
          from entry in frenchNumbers
          where (entry.Key % 2) == 0
          select entry.Value;
    }
}

Using select to create a sequence of each product name.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
public class MainClass {
    public static void Main() {
        List<Product> products = GetProductList();
        var productNames =
            from p in products
            select p.ProductName;
        foreach (var productName in productNames) {
            Console.WriteLine(productName);
        }
    }
    static List<Product> GetProductList() {
        List<Product> empTree = new List<Product>();
        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<Product> {
    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<Product>.rupareTo(Product other) {
        if (other == null)
            return 1;
        if (this.Id > other.Id)
            return 1;
        if (this.Id < other.Id)
            return -1;
        return 0;
    }
}