ThenBy(TSource, TKey) Method (IOrderedEnumerable(TSource), Func(TSource, TKey), IComparer(TKey))

Enumerable.ThenBy<TSource, TKey> Method (IOrderedEnumerable<TSource>, Func<TSource, TKey>, IComparer<TKey>)

[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]

Performs a subsequent ordering of the elements in a sequence in ascending order by using a specified comparer.

Namespace:  System.Linq
Assembly:  System.Core (in System.Core.dll)

public static IOrderedEnumerable<TSource> ThenBy<TSource, TKey>(
	this IOrderedEnumerable<TSource> source,
	Func<TSource, TKey> keySelector,
	IComparer<TKey> comparer
)

Type Parameters

TSource

The type of the elements of source.

TKey

The type of the key returned by keySelector.

Parameters

source
Type: System.Linq.IOrderedEnumerable<TSource>
An IOrderedEnumerable<TElement> that contains elements to sort.
keySelector
Type: System.Func<TSource, TKey>
A function to extract a key from each element.
comparer
Type: System.Collections.Generic.IComparer<TKey>
An IComparer<T> to compare keys.

Return Value

Type: System.Linq.IOrderedEnumerable<TSource>
An IOrderedEnumerable<TElement> whose elements are sorted according to a key.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IOrderedEnumerable<TSource>. When you use instance method syntax to call this method, omit the first parameter.

ExceptionCondition
ArgumentNullException

source or keySelector is null.

This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. The query represented by this method is not executed until the object is enumerated either by calling its GetEnumerator method directly or by using foreach in Visual C# or For Each in Visual Basic.

To order a sequence by the values of the elements themselves, specify the identity function (x => x in Visual C# or Function(x) x in Visual Basic) for keySelector.

Enumerable.ThenBy and Enumerable.ThenByDescending are defined to extend the type IOrderedEnumerable<TElement>, which is also the return type of these methods. This design enables you to specify multiple sort criteria by applying any number of Enumerable.ThenBy or Enumerable.ThenByDescending methods.

NoteNote:

Because IOrderedEnumerable<TElement> inherits from IEnumerable<T>, you can call Enumerable.OrderBy or Enumerable.OrderByDescending on the results of a call to Enumerable.OrderBy, Enumerable.OrderByDescending, Enumerable.ThenBy or Enumerable.ThenByDescending. Doing this introduces a new primary ordering that ignores the previously established ordering.

If comparer is null, the default comparer Default is used to compare keys.

This method performs a stable sort; that is, if the keys of two elements are equal, the order of the elements is preserved. In contrast, an unstable sort does not preserve the order of elements that have the same key.

Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone

Show:
© 2017 Microsoft