Enumerable.OrderBy<TSource, TKey> Method (IEnumerable<TSource>, Func<TSource, TKey>, IComparer<TKey>)
April 12, 2014
Sorts the elements of a sequence in ascending order by using a specified comparer.
Assembly: System.Core (in System.Core.dll)
public static IOrderedEnumerable<TSource> OrderBy<TSource, TKey>( this IEnumerable<TSource> source, Func<TSource, TKey> keySelector, IComparer<TKey> comparer )
The type of the elements of source.
The type of the key returned by keySelector.
- Type: System.Collections.Generic.IEnumerable<>
A sequence of values to order.
- Type: System.Func<, >
A function to extract a key from an element.
Return ValueType: System.Linq.IOrderedEnumerable<>
An IOrderedEnumerable<TElement> whose elements are sorted according to a key.
Usage NoteIn Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable<>. When you use instance method syntax to call this method, omit the first parameter.
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.
Two methods are defined to extend the type IOrderedEnumerable<TElement>, which is the return type of this method. These two methods, namely ThenBy and ThenByDescending, enable you to specify additional sort criteria to sort a sequence. ThenBy and ThenByDescending also return an IOrderedEnumerable<TElement>, which means any number of consecutive calls to ThenBy or ThenByDescending can be made.
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.