Enumerable.OrderByDescending 方法

定义

按降序对序列的元素排序。Sorts the elements of a sequence in descending order.

重载

OrderByDescending<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IComparer<TKey>)

使用指定的比较器按降序对序列的元素排序。Sorts the elements of a sequence in descending order by using a specified comparer.

OrderByDescending<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>)

根据键按降序对序列的元素进行排序。Sorts the elements of a sequence in descending order according to a key.

OrderByDescending<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IComparer<TKey>)

使用指定的比较器按降序对序列的元素排序。Sorts the elements of 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> ^ OrderByDescending(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector, System::Collections::Generic::IComparer<TKey> ^ comparer);
public static System.Linq.IOrderedEnumerable<TSource> OrderByDescending<TSource,TKey> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, System.Collections.Generic.IComparer<TKey> comparer);
public static System.Linq.IOrderedEnumerable<TSource> OrderByDescending<TSource,TKey> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, System.Collections.Generic.IComparer<TKey>? comparer);
static member OrderByDescending : seq<'Source> * Func<'Source, 'Key> * System.Collections.Generic.IComparer<'Key> -> System.Linq.IOrderedEnumerable<'Source>
<Extension()>
Public Function OrderByDescending(Of TSource, TKey) (source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey), comparer As IComparer(Of TKey)) As IOrderedEnumerable(Of TSource)

类型参数

TSource

source 的元素类型。The type of the elements of source.

TKey

keySelector 返回的键的类型。The type of the key returned by keySelector.

参数

source
IEnumerable<TSource>

一个要排序的值序列。A sequence of values to order.

keySelector
Func<TSource,TKey>

用于从元素中提取键的函数。A function to extract a key from an element.

comparer
IComparer<TKey>

用于比较键的 IComparer<T>An IComparer<T> to compare keys.

返回

IOrderedEnumerable<TSource>

一个 IOrderedEnumerable<TElement>,将根据键按降序对其元素进行排序。An IOrderedEnumerable<TElement> whose elements are sorted in descending order according to a key.

例外

sourcekeySelectornullsource or keySelector is null.

示例

下面的代码示例演示如何使用 OrderByDescending<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IComparer<TKey>) 转换函数和自定义比较器按降序对序列的元素进行排序。The following code example demonstrates how to use OrderByDescending<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IComparer<TKey>) to sort the elements of a sequence in descending order by using a transform function and a custom comparer.

/// <summary>
/// This IComparer class sorts by the fractional part of the decimal number.
/// </summary>
public class SpecialComparer : IComparer<decimal>
{
    /// <summary>
    /// Compare two decimal numbers by their fractional parts.
    /// </summary>
    /// <param name="d1">The first decimal to compare.</param>
    /// <param name="d2">The second decimal to compare.</param>
    /// <returns>1 if the first decimal's fractional part
    /// is greater than the second decimal's fractional part,
    /// -1 if the first decimal's fractional
    /// part is less than the second decimal's fractional part,
    /// or the result of calling Decimal.Compare()
    /// if the fractional parts are equal.</returns>
    public int Compare(decimal d1, decimal d2)
    {
        decimal fractional1, fractional2;

        // Get the fractional part of the first number.
        try
        {
            fractional1 = decimal.Remainder(d1, decimal.Floor(d1));
        }
        catch (DivideByZeroException)
        {
            fractional1 = d1;
        }
        // Get the fractional part of the second number.
        try
        {
            fractional2 = decimal.Remainder(d2, decimal.Floor(d2));
        }
        catch (DivideByZeroException)
        {
            fractional2 = d2;
        }

        if (fractional1 == fractional2)
            return Decimal.Compare(d1, d2);
        else if (fractional1 > fractional2)
            return 1;
        else
            return -1;
    }
}

public static void OrderByDescendingEx1()
{
    List<decimal> decimals =
        new List<decimal> { 6.2m, 8.3m, 0.5m, 1.3m, 6.3m, 9.7m };

    IEnumerable<decimal> query =
        decimals.OrderByDescending(num =>
                                       num, new SpecialComparer());

    foreach (decimal num in query)
    {
        Console.WriteLine(num);
    }
}

/*
 This code produces the following output:

 9.7
 0.5
 8.3
 6.3
 1.3
 6.2
*/
' This class provides a custom implementation 
' of the IComparer.Compare() method.
Class SpecialComparer
    Implements IComparer(Of Decimal)
    ''' <summary>
    ''' Compare two decimal numbers by their fractional parts.
    ''' </summary>
    ''' <param name="d1">The first decimal to compare.</param>
    ''' <param name="d2">The second decimal to compare.</param>
    ''' <returns>1 if the first decimal's fractional part is greater than
    ''' the second decimal's fractional part,
    ''' -1 if the first decimal's fractional
    ''' part is less than the second decimal's fractional part,
    ''' or the result of calling Decimal.Compare()
    ''' if the fractional parts are equal.</returns>
    Function Compare(ByVal d1 As Decimal, ByVal d2 As Decimal) As Integer _
    Implements IComparer(Of Decimal).Compare

        Dim fractional1 As Decimal
        Dim fractional2 As Decimal

        ' Get the fractional part of the first number.
        Try
            fractional1 = Decimal.Remainder(d1, Decimal.Floor(d1))
        Catch ex As DivideByZeroException
            fractional1 = d1
        End Try

        ' Get the fractional part of the second number.
        Try
            fractional2 = Decimal.Remainder(d2, Decimal.Floor(d2))
        Catch ex As DivideByZeroException
            fractional2 = d2
        End Try

        If (fractional1 = fractional2) Then
            ' The fractional parts are equal, so compare the entire numbers.
            Return Decimal.Compare(d1, d2)
        ElseIf (fractional1 > fractional2) Then
            Return 1
        Else
            Return -1
        End If
    End Function
End Class

Sub OrderByDescendingEx1()
    ' Create a list of decimal values.
    Dim decimals As New List(Of Decimal)(New Decimal() _
                                     {6.2D, 8.3D, 0.5D, 1.3D, 6.3D, 9.7D})

    ' Order the elements of the list by passing
    ' in the custom IComparer class.
    Dim query As IEnumerable(Of Decimal) =
    decimals.OrderByDescending(Function(num) num,
                               New SpecialComparer())

    Dim output As New System.Text.StringBuilder
    For Each num As Decimal In query
        output.AppendLine(num)
    Next

    ' Display the output.
    Console.WriteLine(output.ToString())
End Sub

' This code produces the following output:
'
' 9.7
' 0.5
' 8.3
' 6.3
' 1.3
' 6.2

注解

此方法是使用延迟执行实现的。This method is implemented by using deferred execution. 即时返回值是一个对象,该对象存储执行操作所需的所有信息。The immediate return value is an object that stores all the information that is required to perform the action. 此方法表示的查询在枚举对象之前不会执行,方法是直接调用其 GetEnumerator 方法,或者通过 foreach 在 Visual c # 中使用或 For Each 在 Visual Basic 中使用。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.

若要按元素本身的值对序列进行排序,请 x => x 在 Visual c # 中指定标识函数 (或 Function(x) x 在 Visual Basic) 中指定 keySelectorTo 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.

定义了两个方法来扩展类型 IOrderedEnumerable<TElement> ,该类型是此方法的返回类型。Two methods are defined to extend the type IOrderedEnumerable<TElement>, which is the return type of this method. 使用这两种方法(即 ThenByThenByDescending ),您可以指定其他排序条件以对序列进行排序。These two methods, namely ThenBy and ThenByDescending, enable you to specify additional sort criteria to sort a sequence. ThenByThenByDescending 还返回 IOrderedEnumerable<TElement> ,这意味着对或的任意连续调用 ThenBy ThenByDescending 都可以进行。ThenBy and ThenByDescending also return an IOrderedEnumerable<TElement>, which means any number of consecutive calls to ThenBy or ThenByDescending can be made.

备注

由于 IOrderedEnumerable<TElement> 继承自 IEnumerable<T> ,因此可以对 OrderBy OrderByDescending 、或调用的结果调用或 OrderBy OrderByDescending ThenBy ThenByDescendingBecause IOrderedEnumerable<TElement> inherits from IEnumerable<T>, you can call OrderBy or OrderByDescending on the results of a call to OrderBy, OrderByDescending, ThenBy or ThenByDescending. 这样做会引入一个新的主要顺序,该顺序将忽略以前建立的排序。Doing this introduces a new primary ordering that ignores the previously established ordering.

如果 comparernull ,则使用默认比较器 Default 对键进行比较。If comparer is null, the default comparer Default is used to compare keys.

此方法执行稳定排序;也就是说,如果两个元素的键相等,则会保留元素的顺序。This method performs a stable sort; that is, if the keys of two elements are equal, the order of the elements is preserved. 与此相反,不稳定排序不会保留具有相同键的元素的顺序。In contrast, an unstable sort does not preserve the order of elements that have the same key.

另请参阅

适用于

OrderByDescending<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>)

根据键按降序对序列的元素进行排序。Sorts the elements of a sequence in descending order according to a key.

public:
generic <typename TSource, typename TKey>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::IOrderedEnumerable<TSource> ^ OrderByDescending(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector);
public static System.Linq.IOrderedEnumerable<TSource> OrderByDescending<TSource,TKey> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector);
static member OrderByDescending : seq<'Source> * Func<'Source, 'Key> -> System.Linq.IOrderedEnumerable<'Source>
<Extension()>
Public Function OrderByDescending(Of TSource, TKey) (source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey)) As IOrderedEnumerable(Of TSource)

类型参数

TSource

source 的元素类型。The type of the elements of source.

TKey

keySelector 返回的键的类型。The type of the key returned by keySelector.

参数

source
IEnumerable<TSource>

一个要排序的值序列。A sequence of values to order.

keySelector
Func<TSource,TKey>

用于从元素中提取键的函数。A function to extract a key from an element.

返回

IOrderedEnumerable<TSource>

一个 IOrderedEnumerable<TElement>,将根据键按降序对其元素进行排序。An IOrderedEnumerable<TElement> whose elements are sorted in descending order according to a key.

例外

sourcekeySelectornullsource or keySelector is null.

注解

此方法是使用延迟执行实现的。This method is implemented by using deferred execution. 即时返回值是一个对象,该对象存储执行操作所需的所有信息。The immediate return value is an object that stores all the information that is required to perform the action. 此方法表示的查询在枚举对象之前不会执行,方法是直接调用其 GetEnumerator 方法,或者通过 foreach 在 Visual c # 中使用或 For Each 在 Visual Basic 中使用。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.

若要按元素本身的值对序列进行排序,请 x => x 在 Visual c # 中指定标识函数 (或 Function(x) x 在 Visual Basic) 中指定 keySelectorTo 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.

有关此方法的示例,请参见 OrderByDescending<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IComparer<TKey>)For an example of this method, see OrderByDescending<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IComparer<TKey>).

定义了两个方法来扩展类型 IOrderedEnumerable<TElement> ,该类型是此方法的返回类型。Two methods are defined to extend the type IOrderedEnumerable<TElement>, which is the return type of this method. 使用这两种方法(即 ThenByThenByDescending ),您可以指定其他排序条件以对序列进行排序。These two methods, namely ThenBy and ThenByDescending, enable you to specify additional sort criteria to sort a sequence. ThenByThenByDescending 还返回 IOrderedEnumerable<TElement> ,这意味着对或的任意连续调用 ThenBy ThenByDescending 都可以进行。ThenBy and ThenByDescending also return an IOrderedEnumerable<TElement>, which means any number of consecutive calls to ThenBy or ThenByDescending can be made.

备注

由于 IOrderedEnumerable<TElement> 继承自 IEnumerable<T> ,因此可以对 OrderBy OrderByDescending 、或调用的结果调用或 OrderBy OrderByDescending ThenBy ThenByDescendingBecause IOrderedEnumerable<TElement> inherits from IEnumerable<T>, you can call OrderBy or OrderByDescending on the results of a call to OrderBy, OrderByDescending, ThenBy or ThenByDescending. 这样做会引入一个新的主要顺序,该顺序将忽略以前建立的排序。Doing this introduces a new primary ordering that ignores the previously established ordering.

此方法使用默认比较器对键进行比较 DefaultThis method compares keys by using the default comparer Default.

此方法执行稳定排序;也就是说,如果两个元素的键相等,则会保留元素的顺序。This method performs a stable sort; that is, if the keys of two elements are equal, the order of the elements is preserved. 与此相反,不稳定排序不会保留具有相同键的元素的顺序。In contrast, an unstable sort does not preserve the order of elements that have the same key.

在查询表达式语法中, orderby descending (Visual c # ) 或 Order By Descending (Visual Basic) 子句转换为对的调用 OrderByDescendingIn query expression syntax, an orderby descending (Visual C#) or Order By Descending (Visual Basic) clause translates to an invocation of OrderByDescending.

另请参阅

适用于