LINQ OrderByDescending

Summary: in this tutorial, you’ll learn how to use the LINQ OrderByDescending() method to sort elements of a sequence in descending order based on a specified key.

Introduction to the LINQ OrderByDescending() method

The OrderByDescending() method sorts elements of a sequence in descending order and returns a new sorted sequence.

The following shows the syntax of the OrderByDescending() method:

public static IOrderedEnumerable<TSource> OrderByDescending<TSource, TKey> (
    this IEnumerable<TSource> source, 
    Func<TSource, TKey> keySelector
);Code language: C# (cs)

In this syntax:

TSource is the type of elements in the source sequence.
TKey is the type of key returned by the keySelector function.
source is the sequence of elements to sort, which is an IEnumerable<T> type.
keySelector is a function to extract a key from an element.

The OrderByDescending() method returns an IOrderedEnumerable<TElement> that contains elements sorted in descending according to a key.

If the source sequence or keySelector function is null, the method throws an ArgumentNullException.

To sort a sequence of elements by a key in ascending order, you use the OrderBy() method instead.

LINQ OrderByDescending() method examples

Let’s take some examples of using the OrderByDescending() method.

1) Using the OrderByDescending() method to sort a sequence of numbers

The following example demonstrates how to use the OrderByDescending() method to sort a sequence of numbers in descending order:

using static System.Console;

int[] numbers = { 3, 1, 4, 0, 5 };

var sortedNumbers = numbers.OrderByDescending(number => number);

foreach (var number in sortedNumbers)
{
    Write($"{number} ");
}Code language: C# (cs)

Output:

5 4 3 1 0Code language: C# (cs)

How it works.

First, declare an array of integers and initialize it with five numbers:

int[] numbers = { 3, 1, 4, 0, 5 };

Second, sort the numbers in the numbers array in descending order using the OrderByDescending() method. The lambda expression number => number returns the number in the numbers array for sorting:

var sortedNumbers = numbers.OrderByDescending(number => number);Code language: JavaScript (javascript)

Third, write the number in the sequence to the console using a foreach loop and Write() method:

foreach (var number in sortedNumbers)
{
    Write($"{number} ");
}Code language: PHP (php)

2) Using the OrderByDescending() method to sort a sequence of strings

The following example uses the OrderByDescending() method to sort an array of strings in descending order:

using static System.Console;

string[] mountains = {
    "Mount Everest",
    "K2",
    "Kangchenjunga",
    "Lhotse",
    "Makalu"
};

var sortedMountains = mountains.OrderByDescending(m => m);

foreach (var mountain in sortedMountains)
{
    WriteLine(mountain);
}Code language: C# (cs)

Output:

Mount Everest
Makalu
Lhotse
Kangchenjunga
K2Code language: C# (cs)

3) Using LINQ OrderByDescending() method to sort a sequence of objects in descending order according to a key

The following program demonstrates how to use the OrderByDescending() method to sort a list of Employee objects by salary in descending order:

using static System.Console;

class Employee
{
    public string? Name { get; set; }
    public string? Department { get; set; }
    public int Salary { get; set; }
}
class Program
{
    public static void Main()
    {
        var employees = new List<Employee>()
        {
                new Employee { Name = "John", Department = "HR", Salary = 50000 },
                new Employee { Name = "Jane", Department = "IT", Salary = 60000 },
                new Employee { Name = "Bob", Department = "HR", Salary = 45000 },
                new Employee { Name = "Sara", Department = "IT", Salary = 55000 },
                new Employee { Name = "Tom", Department = "IT", Salary = 65000 }
            };

        var results = employees.OrderByDescending(e => e.Salary);

        foreach (var employee in results)
        {
            WriteLine($"{employee.Name} - {employee.Salary:C}");
        }
    }
}Code language: C# (cs)

Output:

Tom - $65,000.00
Jane - $60,000.00
Sara - $55,000.00
John - $50,000.00
Bob - $45,000.00Code language: C# (cs)

How it works.

First, define an Employee class that has three properties: Name, Department, and Salary.

class Employee
{
    public string? Name { get; set; }
    public string? Department { get; set; }
    public int Salary { get; set; }
}Code language: C# (cs)

Second, define a list of Employee objects in the Main() method:

var employees = new List<Employee>() 
{
    new Employee { Name = "John", Department = "HR", Salary = 50000 },
    new Employee { Name = "Jane", Department = "IT", Salary = 60000 },
    new Employee { Name = "Bob", Department = "HR", Salary = 45000 },
    new Employee { Name = "Sara", Department = "IT", Salary = 55000 },
    new Employee { Name = "Tom", Department = "IT", Salary = 65000 }
};Code language: C# (cs)

Third, sort the employees list by salary in descending order using the OrderByDescending() method:

 var results = employees.OrderByDescending(e => e.Salary);Code language: C# (cs)

The lambda expression e => e.Salary extracts the Salary value of each Employee object for sorting.

Finally, write the employee information to the console using a foreach loop and WriteLine() method:

foreach (var employee in results)
{
    WriteLine($"{employee.Name} - {employee.Salary:C}");

}Code language: C# (cs)

Summary

Use the LINQ OrderByDescending() method to sort elements of a sequence by a key in descending order.

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