Language Integrated Query (LINQ) is a powerful feature in C# that allows developers to query collections in a concise and readable manner. If you’re working with arrays, lists, or other data structures, LINQ provides a consistent way to filter, sort, and transform your data. In this blog post, we’ll look at how you can use LINQ to filter and sort collections in C#.

1. Introduction to LINQ

LINQ stands for Language Integrated Query, and as the name suggests, it integrates query capabilities directly into the C# language. This means you can write SQL-like queries directly in C# without having to switch to a different syntax or language.

2. Setting Up Your Environment

To use LINQ, you need to ensure you have the necessary namespaces included in your project. The primary namespace for LINQ is System.Linq. So, at the top of your C# file, include:

using System.Linq;

3. Filtering Collections with LINQ

Filtering is one of the most common operations you’ll perform with collections. With LINQ, you can use the Where method to filter collections based on a predicate.

Example:

Suppose you have a list of integers and you want to filter out only the even numbers:

List<int> numbers = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

var evenNumbers = numbers.Where(n => n % 2 == 0);

foreach (var number in evenNumbers)
{
    Console.WriteLine(number);
}

In the example above, the lambda expression n => n % 2 == 0 is the predicate that filters the collection.

4. Sorting Collections with LINQ

Sorting is another common operation. With LINQ, you can use the OrderBy or OrderByDescending methods.

Example:

To sort the list of integers in ascending order:

var sortedNumbers = numbers.OrderBy(n => n);

foreach (var number in sortedNumbers)
{
    Console.WriteLine(number);
}

For descending order:

var sortedNumbersDesc = numbers.OrderByDescending(n => n);

foreach (var number in sortedNumbersDesc)
{
    Console.WriteLine(number);
}

5. Combining Filtering and Sorting

You can chain LINQ methods together to perform multiple operations on a collection. For instance, if you want to filter out even numbers and then sort them in descending order:

var result = numbers.Where(n => n % 2 == 0).OrderByDescending(n => n);

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

6. Advanced Filtering and Sorting

LINQ provides a plethora of methods to cater to more complex scenarios:

• Select: Transforms each element of the collection.
• Skip: Bypasses a specified number of elements in the collection.
• Take: Returns a specified number of contiguous elements from the start of the collection.
• First: Returns the first element of a collection, or the first element that satisfies a condition.
• Last: Returns the last element of a collection, or the last element that satisfies a condition.

Example:

Suppose you have a list of students and you want to get the top 3 students with the highest scores:

public class Student
{
    public string Name { get; set; }
    public int Score { get; set; }
}

List<Student> students = new List<Student>
{
    new Student { Name = "Dan", Score = 85 },
    new Student { Name = "Bob", Score = 90 },
    new Student { Name = "Greg", Score = 80 },
    new Student { Name = "Sue", Score = 95 }
};

var topStudents = students.OrderByDescending(s => s.Score).Take(3);

foreach (var student in topStudents)
{
    Console.WriteLine($"{student.Name}: {student.Score}");
}

7. Conclusion

LINQ is a powerful tool in the C# developer’s toolkit. It provides a consistent and readable way to query collections, making your code more maintainable and expressive.