Part 26 Set operators in LINQ

Text version of the video http://csharp-video-tutorials.blogspot.com/2014/08/part-26-set-operators-in-linq.html Healthy diet is very important both for the body and mind. If you like Aarvi Kitchen recipes, please support by sharing, subscribing and liking our YouTube channel. Hope you can help. https://www.youtube.com/channel/UC7sEwIXM_YfAMyonQCrGfWA/?sub_confirmation=1 Slides http://csharp-video-tutorials.blogspot.com/2014/08/part-26-set-operators-in-linq_9.html LINQ Tutorial - All Text Articles & Slides http://csharp-video-tutorials.blogspot.com/2014/07/linq-tutorial.html LINQ Tutorial Playlist https://www.youtube.com/playlist?list=PL6n9fhu94yhWi8K02Eqxp3Xyh_OmQ0Rp6 Dot Net, SQL, Angular, JavaScript, jQuery and Bootstrap complete courses https://www.youtube.com/user/kudvenkat/playlists?view=1&sort=dd The following operators belong to Set operators category Distinct Union Intersect Except In this video we will discuss Distinct operator. This operator returns distinct elements from a given collection. Example 1: Return distinct country names. In this example the default comparer is being used and the comparison is case-sensitive, so in the output we see country USA 2 times. string[] countries = { "USA", "usa", "INDIA", "UK", "UK" }; var result = countries.Distinct(); foreach (var v in result) { Console.WriteLine(v); } Example 2: For the comparision to be case-insensitive, use the other overloaded version of Distinct() method to which we can pass a class that implements IEqualityComparer as an argument. In this case we see country USA only once in the output. string[] countries = { "USA", "usa", "INDIA", "UK", "UK" }; var result = countries.Distinct(StringComparer.OrdinalIgnoreCase); foreach (var v in result) { Console.WriteLine(v); } When comparing elements, Distinct() works in a slightly different manner with complex types like Employee, Customer etc. Example 3: Notice that in the output we don't get unique employees. This is because, the default comparer is being used which will just check for object references being equal and not the individual property values. List[Employee] list = new List[Employee]() { new Employee { ID = 101, Name = "Mike"}, new Employee { ID = 101, Name = "Mike"}, new Employee { ID = 102, Name = "Mary"} }; var result = list.Distinct(); foreach (var v in result) { Console.WriteLine(v.ID + "\t" + v.Name); } To solve the problem in Example 3, there are 3 ways 1. Use the other overloaded version of Distinct() method to which we can pass a custom class that implements IEqualityComparer 2. Override Equals() and GetHashCode() methods in Employee class 3. Project the properties into a new anonymous type, which overrides Equals() and GetHashCode() methods Example 4 : Using the overloaded version of Distinct() method to which we can pass a custom class that implements IEqualityComparer Step 1 : Create a custom class that implements IEqualityComparer[T] and implement Equals() and GetHashCode() methods public class EmployeeComparer : IEqualityComparer[Employee] { public bool Equals(Employee x, Employee y) { return x.ID == y.ID && x.Name == y.Name; } public int GetHashCode(Employee obj) { return obj.ID.GetHashCode() ^ obj.Name.GetHashCode(); } } Step 2 : Pass an instance of EmployeeComparer as an argument to Distinct() method List[Employee] list = new List[Employee]() { new Employee { ID = 101, Name = "Mike"}, new Employee { ID = 101, Name = "Mike"}, new Employee { ID = 102, Name = "Mary"} }; var result = list.Distinct(new EmployeeComparer()); foreach (var v in result) { Console.WriteLine(v.ID + "\t" + v.Name); } Example 5 : Override Equals() and GetHashCode() methods in Employee class public class Employee { public int ID { get; set; } public string Name { get; set; } public override bool Equals(object obj) { return this.ID == ((Employee)obj).ID && this.Name == ((Employee)obj).Name; } public override int GetHashCode() { return this.ID.GetHashCode() ^ this.Name.GetHashCode(); } } Example 6 : Project the properties into a new anonymous type, which overrides Equals() and GetHashCode() methods List[Employee] list = new List[Employee]() { new Employee { ID = 101, Name = "Mike"}, new Employee { ID = 101, Name = "Mike"}, new Employee { ID = 102, Name = "Mary"} }; var result = list.Select(x =] new { x.ID, x.Name }).Distinct(); foreach (var v in result) { Console.WriteLine(" " + v.ID + "\t" + v.Name); }