LINQ Except in C#

Back to: CSharp LINQ and Lambda Expressions Tutorial

LINQ (Language-Integrated Query) is a powerful technology that allows developers to query and manipulate data in a more efficient and intuitive way. One of the set operators provided by LINQ is Except. The Except operator is used to compare two sequences and retrieve only the elements that are in the first sequence and not in the second. In this lesson, we will discuss the syntax of LINQ Except, its usage, and some examples to better understand its functionality.

Syntax:

The syntax for LINQ Except is as follows:

var result = sequence1.Except(sequence2);

Here, sequence1 and sequence2 are two sequences that we want to compare. The Except() method takes two parameters, which are the two sequences we want to compare, and returns a new sequence with only the elements that are in sequence1 and not in sequence2.

Usage:

The Except operator is useful in scenarios where we need to find the elements in one sequence that are not present in another sequence. For example, suppose we have two lists, one containing the names of employees who work in a particular department, and the other containing the names of employees who work in another department. We want to create a list of employees who work in the first department but not in the second department. In this scenario, we can use the Except operator to compare the two lists and get a new list with only the elements that are in the first list and not in the second.

Examples:

Let’s take a look at some examples to better understand how to use LINQ Except in C#.

Example 1: Finding elements in one integer sequence that are not present in another sequence

int[] sequence1 = { 1, 2, 3, 4, 5 };
int[] sequence2 = { 4, 5, 6, 7, 8 };
var result = sequence1.Except(sequence2);
foreach (int number in result)
{
    Console.WriteLine(number);
}

In this example, we have two integer sequences, sequence1 and sequence2. We use the Except operator to compare the two sequences and store the result in a new sequence called result. The foreach loop iterates through the result sequence and prints the elements that are in sequence1 but not in sequence2.

Example 2: Finding elements in one string sequence that are not present in another sequence

string[] sequence1 = { "John", "Michael", "Samuel", "David" };
string[] sequence2 = { "Samuel", "Mary", "Jennifer", "David" };
var result = sequence1.Except(sequence2, StringComparer.OrdinalIgnoreCase);
foreach (string name in result)
{
    Console.WriteLine(name);
}

In this example, we have two string sequences, sequence1 and sequence2. We use the Except operator to compare the two sequences and store the result in a new sequence called result. The StringComparer.OrdinalIgnoreCase option is used to perform a case-insensitive comparison of string elements. The foreach loop iterates through the result sequence and prints the elements that are in sequence1 but not in sequence2.

FAQs:

Q: What is the difference between Except and Intersect in LINQ?

A: The Except operator retrieves only the elements that are in the first sequence and not in the second, whereas the Intersect operator retrieves only the elements that are common to both sequences.

Q: Can we use Except with non-primitive types?

A: Yes, we can use Except with non-primitive types as long as the type implements the IEqualityComparer interface.

Conclusion:

The Except operator is a useful tool provided by LINQ to find the elements in one sequence that are not present in another sequence. It is an efficient way to retrieve only the elements that are in