Csharp/C Sharp/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);
    }
}

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 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 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;
    }
}

uses 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;
    }
}