LINQ | Set Operator | Except

In LINQ, Set operators are those operators in query expression which return a result set based on the existence or non-existence of the equivalent elements within the same or different collections or sequences or sets. The standard query operator contains the following set operators:

1. Union
2. Intersect
3. Except
4. Distinct

Except Operator

The Except operator returns the set difference. Or in other words, we can say that it returns the set or collection which contain the elements that do not appear in the second collection or set.

• It does not support Query Syntax in C# and VB.Net languages. But you can use Except method on query variable or you can wrap your query in brackets and then call Except method.
• It support method syntax in both C# and VB.Net languages.
• It present in both the Queryable and Enumerable class.
• It is implemented by using deferred execution.
• When you are working with the collections of complex types, then you must use IEqualityComparer interface, otherwise, the Except method will give you incorrect result.

Example 1:

CSharp

// C# program to find the difference
// of the given sequences
using System;
using System.Linq;

class GFG {

    static public void Main()
    {

        // Data source
        char[] sequence1 = {'m', 'q', 'o', 's', 'y', 'a'};
        char[] sequence2 = {'p', 't', 'r', 's', 'y', 'z'};

        // Display the sequences
        Console.WriteLine("Sequence 1 is: ");

        foreach(var s1 in sequence1)
        {
            Console.WriteLine(s1);
        }

        Console.WriteLine("Sequence 2 is: ");

        foreach(var s2 in sequence2)
        {
            Console.WriteLine(s2);
        }

        // Get the difference of the given 
        // sequences Using Except function
        var result = sequence1.Except(sequence2);

        Console.WriteLine("New Sequence: ");

        foreach(var val in result)
        {
            Console.WriteLine(val);
        }
    }
}

Output:

Sequence 1 is: 
m
q
o
s
y
a
Sequence 2 is: 
p
t
r
s
y
z
New Sequence: 
m
q
o
a

Example 2:

CSharp

// C# program to find the languages which is 
// not known by employees of the Department 2
using System;
using System.Linq;
using System.Collections.Generic;

// Employee details
// Department 1
public class Employee1 {

    public int emp_id1
    {
        get;
        set;
    }

    public string emp_name1
    {
        get;
        set;
    }
    public string emp_lang1
    {
        get;
        set;
    }
}

// Employee details
// Department 2
public class Employee2 {

    public int emp_id2
    {
        get;
        set;
    }

    public string emp_name2
    {
        get;
        set;
    }
    public string emp_lang2
    {
        get;
        set;
    }
}

public class GFG {

    // Main method
    static public void Main()
    {
        List<Employee1> emp1 = new List<Employee1>() {

            new Employee1() {emp_id1 = 209, emp_name1 = "Anjita",
                                               emp_lang1 = "C#"},

            new Employee1() {emp_id1 = 210, emp_name1 = "Soniya",
                                                emp_lang1 = "C"},

            new Employee1() {emp_id1 = 211, emp_name1 = "Rohit",
                                            emp_lang1 = "Java"},

        };

        List<Employee2> emp2 = new List<Employee2>() {

            new Employee2() {emp_id2 = 290, emp_name2 = "Anjita",
                                               emp_lang2 = "C#"},

            new Employee2() {emp_id2 = 212, emp_name2 = "MaMa",
                                         emp_lang2 = "Python"},

            new Employee2() {emp_id2 = 233, emp_name2 = "Rima",
                                           emp_lang2 = "Java"},

        };

        // Query to find the languages that is not
        // known by employees of the department 2
        // Using Except method
        var res = emp1.Select(e => e.emp_lang1).Except(emp2.Select(e => e.emp_lang2));
        
        Console.WriteLine("Language: ");
        
        foreach(var val in res)
        {
            Console.WriteLine(val);
        }
    }
}

Output:

Language: 
C

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