Enumerable.ThenByDescending Method
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Performs a subsequent ordering of the elements in a sequence in descending order.
ThenByDescending<TSource,TKey>(IOrderedEnumerable<TSource>, Func<TSource,TKey>) |
Performs a subsequent ordering of the elements in a sequence in descending order, according to a key. |
ThenByDescending<TSource,TKey>(IOrderedEnumerable<TSource>, Func<TSource,TKey>, IComparer<TKey>) |
Performs a subsequent ordering of the elements in a sequence in descending order by using a specified comparer. |
- Source:
- OrderBy.cs
- Source:
- OrderBy.cs
- Source:
- OrderBy.cs
Performs a subsequent ordering of the elements in a sequence in descending order, according to a key.
public:
generic <typename TSource, typename TKey>
[System::Runtime::CompilerServices::Extension]
static System::Linq::IOrderedEnumerable<TSource> ^ ThenByDescending(System::Linq::IOrderedEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector);
public static System.Linq.IOrderedEnumerable<TSource> ThenByDescending<TSource,TKey> (this System.Linq.IOrderedEnumerable<TSource> source, Func<TSource,TKey> keySelector);
static member ThenByDescending : System.Linq.IOrderedEnumerable<'Source> * Func<'Source, 'Key> -> System.Linq.IOrderedEnumerable<'Source>
<Extension()>
Public Function ThenByDescending(Of TSource, TKey) (source As IOrderedEnumerable(Of TSource), keySelector As Func(Of TSource, TKey)) As IOrderedEnumerable(Of TSource)
Type Parameters
- TSource
The type of the elements of source
.
- TKey
The type of the key returned by keySelector
.
Parameters
- source
- IOrderedEnumerable<TSource>
An IOrderedEnumerable<TElement> that contains elements to sort.
- keySelector
- Func<TSource,TKey>
A function to extract a key from each element.
Returns
An IOrderedEnumerable<TElement> whose elements are sorted in descending order according to a key.
Exceptions
source
or keySelector
is null
.
Remarks
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 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 C# or Function(x) x
in Visual Basic) for keySelector
.
ThenBy and 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 ThenBy or ThenByDescending methods.
Note
Because IOrderedEnumerable<TElement> inherits from IEnumerable<T>, you can call OrderBy or OrderByDescending on the results of a call to OrderBy, OrderByDescending, ThenBy or ThenByDescending. Doing this introduces a new primary ordering that ignores the previously established ordering.
This sorting method compares keys by using the default comparer Default.
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.
In C# query expression syntax, an orderby [first criterion], [second criterion] descending
clause translates to an invocation of ThenByDescending.
In Visual Basic query expression syntax, an Order By [first criterion], [second criterion] Descending
clause translates to an invocation of ThenByDescending.
See also
Applies to
.NET 9 and other versions
Product | Versions |
---|---|
.NET | Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9 |
.NET Framework | 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
.NET Standard | 1.0, 1.1, 1.2, 1.3, 1.4, 1.6, 2.0, 2.1 |
UWP | 10.0 |
- Source:
- OrderBy.cs
- Source:
- OrderBy.cs
- Source:
- OrderBy.cs
Performs a subsequent ordering of the elements in a sequence in descending order by using a specified comparer.
public:
generic <typename TSource, typename TKey>
[System::Runtime::CompilerServices::Extension]
static System::Linq::IOrderedEnumerable<TSource> ^ ThenByDescending(System::Linq::IOrderedEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector, System::Collections::Generic::IComparer<TKey> ^ comparer);
public static System.Linq.IOrderedEnumerable<TSource> ThenByDescending<TSource,TKey> (this System.Linq.IOrderedEnumerable<TSource> source, Func<TSource,TKey> keySelector, System.Collections.Generic.IComparer<TKey> comparer);
public static System.Linq.IOrderedEnumerable<TSource> ThenByDescending<TSource,TKey> (this System.Linq.IOrderedEnumerable<TSource> source, Func<TSource,TKey> keySelector, System.Collections.Generic.IComparer<TKey>? comparer);
static member ThenByDescending : System.Linq.IOrderedEnumerable<'Source> * Func<'Source, 'Key> * System.Collections.Generic.IComparer<'Key> -> System.Linq.IOrderedEnumerable<'Source>
<Extension()>
Public Function ThenByDescending(Of TSource, TKey) (source As IOrderedEnumerable(Of TSource), keySelector As Func(Of TSource, TKey), comparer As IComparer(Of TKey)) As IOrderedEnumerable(Of TSource)
Type Parameters
- TSource
The type of the elements of source
.
- TKey
The type of the key returned by keySelector
.
Parameters
- source
- IOrderedEnumerable<TSource>
An IOrderedEnumerable<TElement> that contains elements to sort.
- keySelector
- Func<TSource,TKey>
A function to extract a key from each element.
- comparer
- IComparer<TKey>
An IComparer<T> to compare keys.
Returns
An IOrderedEnumerable<TElement> whose elements are sorted in descending order according to a key.
Exceptions
source
or keySelector
is null
.
Examples
The following code example demonstrates how to use ThenByDescending<TSource,TKey>(IOrderedEnumerable<TSource>, Func<TSource,TKey>, IComparer<TKey>) to perform a secondary ordering of the elements in a sequence in descending order by using a custom comparer.
public class CaseInsensitiveComparer : IComparer<string>
{
public int Compare(string x, string y)
{
return string.Compare(x, y, true);
}
}
public static void ThenByDescendingEx1()
{
string[] fruits = { "apPLe", "baNanA", "apple", "APple", "orange", "BAnana", "ORANGE", "apPLE" };
// Sort the strings first ascending by their length and
// then descending using a custom case insensitive comparer.
IEnumerable<string> query =
fruits
.OrderBy(fruit => fruit.Length)
.ThenByDescending(fruit => fruit, new CaseInsensitiveComparer());
foreach (string fruit in query)
{
Console.WriteLine(fruit);
}
}
/*
This code produces the following output:
apPLe
apple
APple
apPLE
orange
ORANGE
baNanA
BAnana
*/
' This class provides a custom implementation of the Compare() method.
Class CaseInsensitiveComparer
Implements IComparer(Of String)
Function Compare(ByVal x As String, ByVal y As String) As Integer _
Implements IComparer(Of String).Compare
' Compare values and ignore case.
Return String.Compare(x, y, True)
End Function
End Class
Sub ThenByDescendingEx1()
Dim fruits() As String =
{"apPLe", "baNanA", "apple", "APple", "orange", "BAnana", "ORANGE", "apPLE"}
' Sort the strings first by their length and then
' by using a custom "case insensitive" comparer.
Dim query As IEnumerable(Of String) =
fruits _
.OrderBy(Function(fruit) fruit.Length) _
.ThenByDescending(Function(fruit) fruit, New CaseInsensitiveComparer())
' Display the results.
Dim output As New System.Text.StringBuilder
For Each fruit As String In query
output.AppendLine(fruit)
Next
Console.WriteLine(output.ToString())
End Sub
' This code produces the following output:
' apPLe
' apple
' APple
' apPLE
' orange
' ORANGE
' baNanA
' BAnana
Remarks
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 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 C# or Function(x) x
in Visual Basic) for keySelector
.
ThenBy and 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 ThenBy or ThenByDescending methods.
Note
Because IOrderedEnumerable<TElement> inherits from IEnumerable<T>, you can call OrderBy or OrderByDescending on the results of a call to OrderBy, OrderByDescending, ThenBy or 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.
Applies to
.NET 9 and other versions
Product | Versions |
---|---|
.NET | Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9 |
.NET Framework | 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
.NET Standard | 1.0, 1.1, 1.2, 1.3, 1.4, 1.6, 2.0, 2.1 |
UWP | 10.0 |
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