ThenByDescendinge

ThenByDescending is a method in the LINQ (Language Integrated Query) library of the .NET framework, used for sorting data in a descending order based on a secondary criterion after a primary sort has been applied. It is typically used in conjunction with the OrderBy or ThenBy methods to create more complex sorting logic.

The ThenByDescending method is an extension method that operates on an IOrderedEnumerable<T> object, which is the result of a previous sorting operation. It takes a single parameter, which is a lambda expression or a function delegate that specifies the key to sort by in descending order.

For example, consider a list of students with properties for their name and grade. To sort the students first by grade in ascending order and then by name in descending order, you would use the OrderBy method followed by the ThenByDescending method:

var sortedStudents = students.OrderBy(s => s.Grade).ThenByDescending(s => s.Name);

In this example, the students are first sorted by their grade in ascending order. Then, within each grade group, the students are sorted by their name in descending order.

ThenByDescending is particularly useful when you need to sort data based on multiple criteria, allowing for more granular control over the sorting order. It is a versatile method that can be used with various data types and sorting requirements.