Understanding LINQ's let operator in C#

LINQ (Language-Integrated Query) in C# is a powerful tool for querying and manipulating collections. Among its features, the let operator stands out as a versatile tool for creating more readable and maintainable queries. In this advanced blog post, we’ll delve into the intricacies of the let operator with practical examples.

Understanding the let Operator

The let operator allows you to create a temporary variable within a LINQ query. This variable is accessible within the rest of the query, making it a handy tool for simplifying complex expressions and enhancing the overall readability of your code.

Basic Usage of let

Let’s start with a simple example to illustrate the basic usage of the let operator. Consider a scenario where you have a collection of numbers, and you want to filter out the even numbers and square the remaining ones.

List<int> numbers = new List<int> { 1, 2, 3, 4, 5 };

var query = from num in numbers
            where num % 2 != 0
            let squared = num * num // The let operator creates a temporary variable
            select squared;

foreach (var result in query)

In this example, the let operator is used to create a temporary variable (squared) to hold the result of squaring each odd number. This enhances code readability by separating the logic of squaring from the main query.

Advanced Example with let

Now, let’s explore a more advanced example involving multiple collections. Suppose you have a list of students with their grades and a list of courses. Your goal is to find the average grade for each course.

class Student
    public string Name { get; set; }
    public List<int> Grades { get; set; }

List<Student> students = new List<Student>
    new Student { Name = "John", Grades = new List<int> { 85, 90, 88 } },
    new Student { Name = "Jane", Grades = new List<int> { 92, 88, 95 } },
    new Student { Name = "Bob", Grades = new List<int> { 78, 85, 80 } }

List<string> courses = new List<string> { "Math", "English", "Science" };

var query = from course in courses
            let totalGrade = (from student in students
                              select student.Grades[courses.IndexOf(course)]).Sum()
            let averageGrade = totalGrade / (double)students.Count
            select new
                Course = course,
                AverageGrade = averageGrade

foreach (var result in query)
    Console.WriteLine($"Course: {result.Course}, Average Grade: {result.AverageGrade:F2}");

In this example, the let operator is used to calculate the total grade and average grade for each course, making the query more modular and easier to understand. The temporary variables (totalGrade and averageGrade) enhance the clarity of the code.


The let operator in LINQ is a valuable tool for creating more expressive and readable queries. By introducing temporary variables, you can break down complex expressions, improve code organization, and make your queries more maintainable. Understanding and mastering the let operator can significantly elevate your LINQ skills.

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