Linq- Union, Intersect and Except operators

Union combines two collections into one collection while removing the duplicate elements.

Example 1: numbers1 and numbers2 collections are combined into a single collection. Notice that, the duplicate elements are removed.

int[] numbers1 = { 1, 2, 3, 4, 5 };

int[] numbers2 = { 1, 3, 6, 7, 8 };

var result = numbers1.Union(numbers2);

foreach (var v in result)

{

    Console.WriteLine(v);

}

When comparing elements, just like Distinct() method, Union(), Intersect() and Except() methods work in a slightly different manner with complex types like Employee, Customer etc. 

Example 2 : Notice that in the output the duplicate employee objects are not removed. 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> list1 = new List<Employee>()

{

    new Employee { ID = 101, Name = "Mike"},

    new Employee { ID = 102, Name = "Susy"},

    new Employee { ID = 103, Name = "Mary"}

};

List<Employee> list2 = new List<Employee>()

{

    new Employee { ID = 101, Name = "Mike"},

    new Employee { ID = 104, Name = "John"}

};

var result = list1.Union(list2);

foreach (var v in result)

{

    Console.WriteLine(v.ID + "\t" + v.Name);

}

Example 3 : To solve the problem in Example 2, there are 3 ways
1. Use the other overloaded version of Union() 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

Project the properties into a new anonymous type, which overrides Equals() and GetHashCode() methods

List<Employee> list1 = new List<Employee>()

{

    new Employee { ID = 101, Name = "Mike"},

    new Employee { ID = 102, Name = "Susy"},

    new Employee { ID = 103, Name = "Mary"}

};

List<Employee> list2 = new List<Employee>()

{

    new Employee { ID = 101, Name = "Mike"},

    new Employee { ID = 104, Name = "John"}

};

var result = list1.Select(x => new { x.ID, x.Name })

                    .Union(list2.Select(x => new { x.ID, x.Name }));

foreach (var v in result)

{

    Console.WriteLine(v.ID + "\t" + v.Name);

}

Intersect() returns the common elements between the 2 collections.

Example 4 : Return common elements in numbers1 and numbers2 collections.

int[] numbers1 = { 1, 2, 3, 4, 5 };

int[] numbers2 = { 1, 3, 6, 7, 8 };

var result = numbers1.Intersect(numbers2);

foreach (var v in result)

{

    Console.WriteLine(v);

}

Except() returns the elements that are present in the first collection but not in the second collection.

Example 5: Return the elements that are present in the first collection but not in the second collection.

int[] numbers1 = { 1, 2, 3, 4, 5 };

int[] numbers2 = { 1, 3, 6, 7, 8 };

var result = numbers1.Except(numbers2);

foreach (var v in result)

{

    Console.WriteLine(v);

}

Posted in: LINQ