LinQ Operation

Introduction

Hi everybody, here in this article I want to raise a few basic things regarding the Distinct() extension method in “System.Linq” and we will explain how to customize our Distinct() method using "IEqualityComparer".

Creating Console Application

Let's create a console application for me its “UnderstandingDistinct” and let's create a custom class called “Student” with the following properties:

public class Student

{

public int StudentID { get; set; }

public string StudentName { get; set; }

public string Country { get; set; }

public string City { get; set; }

}

Let's go ahead and do a distinct operation on the collection of the student objects. The following is the code to create a collection of custom objects and do a Distinct() operation in program.cs.

class Program

{

static void Main(string[] args)

{

var studentList = new List<Student>()

{

new Student{ StudentID = 1, City = "BBSR", Country = "India", StudentName = "Mukesh" },

new Student{ StudentID = 2, City = "BBSR", Country = "India", StudentName = "Abhishek"},

new Student{ StudentID = 3, City = "BBSR", Country = "India", StudentName = "Sachin"},

new Student{ StudentID = 4, City = "BLR", Country = "India", StudentName = "Richi"},

new Student{ StudentID = 5, City = "BLR", Country = "India", StudentName = "Nibedita"},

};

var distinctStudentList = studentList.Distinct();

//Looping through student list

foreach (var stud in distinctStudentList)

{

Console.WriteLine(stud.StudentName);

}

}

}

On execution of the program we will get the following output:

That's normal, but let's suppose we have a scenario where we want to have all student objects with a distinct country and city from the list. We can see in the editor itsef that we have 2 extensions to this distinct extension method and they are as follows:

And to have a distinct collection on country and city we can use the second extension but before using that we need to create our own custom IEqualityComparer. Let's create a class named “StudentComparer” and this class must implement “IEqualityComparer”. Finally the class will look like:

public class StudentComparer : IEqualityComparer<Student>

{

public bool Equals(Student x, Student y)

{

}

public int GetHashCode(Student obj)

{

}

}

The “IEqualityComparer” interface implements the 2 functions “bool Equals(Student x, Student y)” and “int GetHashCode(Student obj)” and these 2 functions decide the equality between student objects. Since we are trying to have distinct on 2 factors that are the country and city properties of a student object, let's add our logic to these 2 functions and our custom logic will look like: