LINQ | Set Operator | Union

In LINQ, Set operators are those operators in query expression which return a result set which is 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

Union

The Union operator returns the set union. Or in other words, we can say that it returns the set which contains the unique elements that appear in the given input collections, or sequence.

• It does not support query syntax in C# and VB.Net languages. But you can use Union method on query variable or you can wrap your query in brackets and then the call Union 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 you must use IEqualityComparer interface, otherwise, the Union method will give you incorrect result.

Example 1:

// C# program to find the union
// of the given sequence
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', 'w', '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 union of the given sequence
        // Using Union function
        var result = sequence1.Union(sequence2);

        Console.WriteLine("Unique 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
w
z
Unique Sequence: 
m
q
o
s
y
a
p
t
r
w
z

Example 2:

// C# program to find the common
// languages known by the employees
using System;
using System.Linq;
using System.Collections.Generic;

// Employee details
public class Employee1 {

    public int emp_id1
    {
        get;
        set;
    }

    public string emp_name1
    {
        get;
        set;
    }
    public string emp_lang1
    {
        get;
        set;
    }
}
// Employee details
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 common languages
        // known by the employees
        // Using Union method
        var res = emp1.Select(e => e.emp_lang1).Union(emp2.Select(e => e.emp_lang2));

        Console.WriteLine("Common Languages: ");

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

Output:

Common Languages: 
C#
C
Java
Python