C# LINQ Introduction

Sort with OrderBy

A common use case is sorting.

For that LINQ offers

• OrderBy(keySelector) and
• OrderByDescending(keySelector)

Having the possibility to select a key is very helpful, when we want to order objects. This way, we can easily order our people by age:

var people = new List<Person> {
    new Person { Name = "...", Age = 5 },
    new Person { Name = "...", Age = 8 },
    new Person { Name = "...", Age = 3 },
}

var sortedPeople = people.OrderBy(p => p.Age);

We can also sort the objects by multiple keys, e.g. first by Age and then by Name. After calling OrderBy we get new LINQ methods to chain:

• ThenBy(keySelector) and
• ThenByDescending(keySelector)

Note: Calling OrderBy twice would not lead to the expected result, because the second call to OrderBy would sort the whole collection again. Instead, calling OrderBy followed by ThenBy leads to the expected result, because ThenBy performs a subsequent ordering.