The method matches instances of a pattern and is used to extract value based on a pattern.Let us see hoe to check for a valid URL.For that, pass the regex expression in the Matches method.MatchCollection mc = Regex.Matches(text, expr);Above, the expr is our expression that we have set to check for valid URL."^(http|http(s)?://)?([\w-]+\.)+[\w-]+[.com|.in|.org]+(\[\?%&=]*)?”The text we have set to check is a URL i.e.https://demo.comLet us see the complete code.Example Live Demousing System; using System.Text.RegularExpressions; namespace Demo {    class Program {       private static void showMatch(string text, string expr) {          MatchCollection mc = Regex.Matches(text, expr);   ... Read More

Use the FirstorDefault() method to return the first element of a sequence or a default value if element isn’t there.The following is our empty list −List val = new List { };Now, we cannot display the first element, since it is an empty collection. For that, use the FirstorDefault() method to display the default value.val.AsQueryable().FirstOrDefault();The following is the complete example.Example Live Demousing System; using System.Collections.Generic; using System.Linq; class Demo {    static void Main() {       List val = new List { };       double d = val.AsQueryable().FirstOrDefault();       Console.WriteLine("Default Value = "+d);     ... Read More

Find common elements between two arrays using the Intersect() method.The following are our arrays −int[] val1 = { 15, 20, 40, 60, 75, 90 }; int[] val2 = { 17, 25, 35, 55, 75, 90 };To perform intersection.val1.AsQueryable().Intersect(val2);Let us see the entire example.Example Live Demousing System; using System.Collections.Generic; using System.Linq; class Demo {    static void Main() {       int[] val1 = { 15, 20, 40, 60, 75, 90 };       int[] val2 = { 17, 25, 35, 55, 75, 90 };       IEnumerable res = val1.AsQueryable().Intersect(val2);       Console.WriteLine("Intersection of both the lists...");       foreach (int a in res)       Console.WriteLine(a);    } }OutputIntersection of both the lists... 75 90

To cast a specific type to its IEnumerable equivalent, use the AsEnumerable() method. It is an extension method.The following is our array −int[] arr = new int[5]; arr[0] = 10; arr[1] = 20; arr[2] = 30; arr[3] = 40; arr[4] = 50;Now, get the IEnumerable equivalent.arr.AsEnumerable();Example Live Demousing System; using System.Linq; class Demo {    static void Main() {       int[] arr = new int[5];       arr[0] = 10;       arr[1] = 20;       arr[2] = 30;       arr[3] = 40;       arr[4] = 50;       var res = arr.AsEnumerable();       foreach (var ele in res) {          Console.WriteLine(ele);       }    } }Output10 20 30 40 50

The following are our strings in a list −List list = new List { "keyboard", "mouse", "joystick", "monitor" };To use the first 3 letters, use substring method and use it under the Linq Select method.IEnumerable res = list.AsQueryable() .Cast() .Select(str => str.Substring(0, 3));Example Live Demousing System; using System.Linq; using System.Collections.Generic; class Demo {    static void Main() {       List list = new List { "keyboard", "mouse", "joystick", "monitor" };       // getting first 3 letters from every string       IEnumerable res = list.AsQueryable() .Cast() .Select(str =>       str.Substring(0,3));       foreach (string str in res) {          Console.WriteLine(str);       }    } }Outputkey mou joy mon

To handle empty collections, use the DefaultIfEmpty() method in C#.If an array is empty, then using this method will show the default method instead of displaying an error.Let’s say we have an empty list.List myList = new List();Now, use DefaultIfEmpty() method to display the default value.myList.DefaultIfEmpty();Example Live Demousing System; using System.Linq; using System.Collections.Generic; class Demo {    static void Main() {       List myList = new List();       var res = myList.DefaultIfEmpty();       foreach (var a in res) {          Console.WriteLine(a);       }    } }Output0

Set a sequence and add elements.List ID = new List { 120, 111, 250, 111, 120, 300, 399, 450 };Use Distinct() method to get distinct element from the above list.IEnumerable res = ID.AsQueryable().Distinct();Let us see the complete code.Example Live Demousing System; using System.Linq; using System.Collections.Generic; class Demo {    static void Main() {       List ID = new List { 120, 111, 250, 111, 120, 300, 399, 450 };       // get distinct elements       IEnumerable res = ID.AsQueryable().Distinct();       foreach (int arr in res) {          Console.WriteLine(arr);       }    } }Output120 111 250 300 399 450

The following is our Dictionary with some elements −Dictionary d = new Dictionary() {    {1,"Electronics"},    {2, "Clothing"},    {3,"Toys"},    {4,"Footwear"},    {5, "Accessories"} };Now to display the first element, set the key like this.d[1];The above displays the first element.Example Live Demousing System; using System.Collections.Generic; public class Program {    public static void Main() {       Dictionary d = new Dictionary() {          {1,"Electronics"},          {2, "Clothing"},          {3,"Toys"},          {4,"Footwear"},          {5, "Accessories"}       };       foreach (KeyValuePair ele in d) {          Console.WriteLine("Key = {0}, Value = {1}", ele.Key, ele.Value);       }       Console.WriteLine("First element: "+d[1]);    } }OutputKey = 1, Value = Electronics Key = 2, Value = Clothing Key = 3, Value = Toys Key = 4, Value = Footwear Key = 5, Value = Accessories First element: Electronics

To add key-value pair in C# Dictionary, firstly declare a Dictionary.IDictionary d = new Dictionary();Now, add elements with KeyValuePair.d.Add(new KeyValuePair(1, "TVs")); d.Add(new KeyValuePair(2, "Appliances")); d.Add(new KeyValuePair(3, "Mobile"));After adding elements, let us display the key-value pair.Example Live Demousing System; using System.Collections.Generic; public class Demo {    public static void Main() {       IDictionary d = new Dictionary();       d.Add(new KeyValuePair(1, "TVs"));       d.Add(new KeyValuePair(2, "Appliances"));       d.Add(new KeyValuePair(3, "Mobile"));       d.Add(new KeyValuePair(4, "Tablet"));       d.Add(new KeyValuePair(5, "Laptop"));       d.Add(new KeyValuePair(6, "Desktop"));       d.Add(new KeyValuePair(7, "Hard Drive")); ... Read More

Clear a Hashtable, using the Clear() method in C#.The following is our Hashtable −Hashtable h = new Hashtable(); h.Add(1, "Amit"); h.Add(2, "Sachin"); h.Add(3, "Rahul");Use the clear method.h.Clear();If you will now try to display the Hashtable, nothing would get display since the Hashtable is empty.Example Live Demousing System; using System.Collections; public class Demo {    public static void Main() {       Hashtable h = new Hashtable();       h.Add(1, "Amit");       h.Add(2, "Sachin");       h.Add(3, "Rahul");       Console.WriteLine("Keys and Values list:");       foreach (var key in h.Keys ) {     ... Read More