OrderBy

Note:: Sort collections by order

The OrderBy method is used to sort collections in ascending order.

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

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

In the above example the OrderBy method sorts the numbers in ascending order.
The lamda expression (n => n) is used to specify that we want to sort the numbers by their own value.

OrderByDescending

To order by descending you can use OrderByDescending() like this -

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

Ordering Complex Types

The OrderBy methods also work with complex types and allows you to specify the property to sort by -

public class Employee
{
    public string Name { get; set; }
    public int Age { get; set; }
}

List<Employee> employees = new List<Employee>
{
    new Employee { Name = "Steve", Age = 50 },
    new Employee { Name = "Bill", Age = 55 },
    new Employee { Name = "Lucy", Age = 30 }
};

var sortedEmployees = employees.OrderBy(e => e.Name);

This would sort the employees by their name in ascending order.

ThenBy

ThenBy allows you to sort by further properties once it has been sorted by the initial property.

using System;
using System.Linq;
using System.Collections.Generic;

public class Employee
{
    public string Department { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
}

public class Program
{
    public static void Main()
    {
        List<Employee> employees = new List<Employee>
        {
            new Employee { Department = "HR", Name = "Steve", Age = 50 },
            new Employee { Department = "HR", Name = "Bill", Age = 55 },
            new Employee { Department = "Marketing", Name = "Lucy", Age = 30 },
            new Employee { Department = "HR", Name = "Anna", Age = 40 },
            new Employee { Department = "Marketing", Name = "Mike", Age = 35 }
        };

        var sortedEmployees = employees.OrderBy(e => e.Department).ThenBy(e => e.Name);

        foreach (var employee in sortedEmployees)
        {
            Console.WriteLine(employee.Department + ", " + employee.Name + ", " + employee.Age);
        }
    }
}

In the above example, the employees are sorted by Department using OrderBy. Then within each department, they are sorted by their name alphabetically.

Last modified: 23 September 2024