Set operator: Distinct

The following table lists all Set operators available in LINQ.

Set Operators Usage
Distinct Returns distinct values from a collection.
Except Returns the difference between two sequences, which means the elements of one collection that do not appear in the second collection.
Intersect Returns the intersection of two sequences, which means elements that appear in both the collections.
Union Returns unique elements from two sequences, which means unique elements that appear in either of the two sequences.

The following figure shows how each set operators works on the collections:

LINQ Set operators

Distinct:

The Distinct extension method returns a new collection of unique elements from the given collection.

Example: Distinct C#
            
IList<string> strList = new List<string>(){ "One", "Two", "Three", "Two", "Three" };

IList<int> intList = new List<int>(){ 1, 2, 3, 2, 4, 4, 3, 5 };

var distinctList1 = strList.Distinct();

foreach(var str in distinctList1)
    Console.WriteLine(str);

var distinctList2 = intList.Distinct();

foreach(var i in distinctList2)
    Console.WriteLine(i);

Output:
One
Two
Three
1
2
3
4
5

The Distinct extension method doesn't compare values of complex type objects. You need to implement IEqualityComparer<T> interface in order to compare the values of complex types. In the following example, StudentComparer class implements IEqualityComparer<Student> to compare Student< objects.

Example: Implement IEqualityComparer in C#

public class Student 
{
    public int StudentID { get; set; }
    public string StudentName { get; set; }
    public int Age { get; set; }
}

class StudentComparer : IEqualityComparer<Student>
{
    public bool Equals(Student x, Student y)
    {
        if (x.StudentID == y.StudentID 
                && x.StudentName.ToLower() == y.StudentName.ToLower())
            return true;

        return false;
    }

    public int GetHashCode(Student obj)
    {
        return obj.StudentID.GetHashCode();
    }
}

Now, you can pass an object of the above StudentComparer class in the Distinct() method as a parameter to compare the Student objects as shown below.

Example: Distinct in C#
    
IList<Student> studentList = new List<Student>() { 
        new Student() { StudentID = 1, StudentName = "John", Age = 18 } ,
        new Student() { StudentID = 2, StudentName = "Steve",  Age = 15 } ,
        new Student() { StudentID = 3, StudentName = "Bill",  Age = 25 } ,
        new Student() { StudentID = 3, StudentName = "Bill",  Age = 25 } ,
        new Student() { StudentID = 3, StudentName = "Bill",  Age = 25 } ,
        new Student() { StudentID = 3, StudentName = "Bill",  Age = 25 } ,
        new Student() { StudentID = 5, StudentName = "Ron" , Age = 19 } 
    };


var distinctStudents = studentList.Distinct(new StudentComparer()); 

foreach(Student std in distinctStudents)
    Console.WriteLine(std.StudentName);
    
Output:
John
Steve
Bill
Ron

Distinct operator in Query Syntax:

The Distinct operator is Not Supported in C# Query syntax. However, you can use Distinct method of query variable or wrap whole query into brackets and then call Distinct().

Use the Distinct keyword in VB.Net query syntax:

Example: Distinct in query syntax VB.Net

Dim strList = New List(Of string) From {"One", "Three", "Two", "Two", "One" }

Dim distinctStr = From s In strList _
                  Select s Distinct