Enumerable.OrderByDescending Enumerable.OrderByDescending Enumerable.OrderByDescending Enumerable.OrderByDescending Method

定義

シーケンスの要素を降順に並べ替えます。Sorts the elements of a sequence in descending order.

オーバーロード

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

指定された比較子を使用してシーケンスの要素を降順に並べ替えます。Sorts the elements of a sequence in descending order by using a specified comparer.

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

シーケンスの要素をキーに従って降順に並べ替えます。Sorts the elements of a sequence in descending order according to a key.

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

指定された比較子を使用してシーケンスの要素を降順に並べ替えます。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);
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)

型パラメーター

TSource

source の要素の型。The type of the elements of source.

TKey

keySelector によって返されるキーの型。The type of the key returned by keySelector.

パラメーター

source
IEnumerable<TSource>

順序付ける値のシーケンス。A sequence of values to order.

keySelector
Func<TSource,TKey>

要素からキーを抽出する関数。A function to extract a key from an element.

comparer
IComparer<TKey>

キーを比較する IComparer<T>An IComparer<T> to compare keys.

戻り値

要素がキーに従って降順に並べ替えられている IOrderedEnumerable<TElement>An IOrderedEnumerable<TElement> whose elements are sorted in descending order according to a key.

例外

source または keySelectornull です。source or keySelector is null.

次のコード例は、使用する方法を示しますOrderByDescending<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IComparer<TKey>)変換関数およびカスタム comparer を使用して降順のシーケンスの要素を並べ替えます。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.
    MsgBox(output.ToString())
End Sub

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

注釈

このメソッドは、遅延実行を使用して実装されます。This method is implemented by using deferred execution. 即時の戻り値は、操作を実行するために必要なすべての情報を格納するオブジェクトです。The immediate return value is an object that stores all the information that is required to perform the action. か、呼び出すことによって、オブジェクトが列挙されるまで、このメソッドによって表されるクエリは実行されません、GetEnumeratorメソッドを使用して直接またはforeachVisual C# またはFor EachVisual Basic で。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.

を、要素自体の値によって、シーケンスを順序付けるに identity 関数を指定します (x => x Visual C# またはFunction(x) xVisual Basic) の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.

型を拡張する 2 つのメソッドが定義されているIOrderedEnumerable<TElement>、これは、このメソッドの戻り値の型。Two methods are defined to extend the type IOrderedEnumerable<TElement>, which is the return type of this method. これら 2 つの方法では、namelyThenByThenByDescendingシーケンスを並べ替えるには、追加の並べ替え条件を指定できます。These two methods, namely ThenBy and ThenByDescending, enable you to specify additional sort criteria to sort a sequence. ThenBy ThenByDescendingを返すことも、 IOrderedEnumerable<TElement>、つまり、任意の数を連続して呼び出すのThenByまたはThenByDescending行んだことができます。ThenBy and ThenByDescending also return an IOrderedEnumerable<TElement>, which means any number of consecutive calls to ThenBy or ThenByDescending can be made.

注意

IOrderedEnumerable<TElement>継承IEnumerable<T>、呼び出すことができますOrderByまたはOrderByDescendingへの呼び出しの結果にOrderByOrderByDescendingThenByまたはThenByDescendingします。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. これを行うには、新しいプライマリ順序を以前に確立された順序を無視するが導入されています。Doing this introduces a new primary ordering that ignores the previously established ordering.

場合comparernull、既定の比較子Defaultキーを比較するために使用します。If comparer is null, the default comparer Default is used to compare keys.

このメソッドは、安定した並べ替え; を実行します。つまり、2 つの要素のキーが等しい場合は、要素の順序が保持されます。This method performs a stable sort; that is, if the keys of two elements are equal, the order of the elements is preserved. これに対し、不安定な並べ替えは、同じキーを持つ要素の順序は保持されません。In contrast, an unstable sort does not preserve the order of elements that have the same key.

こちらもご覧ください

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

シーケンスの要素をキーに従って降順に並べ替えます。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)

型パラメーター

TSource

source の要素の型。The type of the elements of source.

TKey

keySelector によって返されるキーの型。The type of the key returned by keySelector.

パラメーター

source
IEnumerable<TSource>

順序付ける値のシーケンス。A sequence of values to order.

keySelector
Func<TSource,TKey>

要素からキーを抽出する関数。A function to extract a key from an element.

戻り値

要素がキーに従って降順に並べ替えられている IOrderedEnumerable<TElement>An IOrderedEnumerable<TElement> whose elements are sorted in descending order according to a key.

例外

source または keySelectornull です。source or keySelector is null.

注釈

このメソッドは、遅延実行を使用して実装されます。This method is implemented by using deferred execution. 即時の戻り値は、操作を実行するために必要なすべての情報を格納するオブジェクトです。The immediate return value is an object that stores all the information that is required to perform the action. か、呼び出すことによって、オブジェクトが列挙されるまで、このメソッドによって表されるクエリは実行されません、GetEnumeratorメソッドを使用して直接またはforeachVisual C# またはFor EachVisual Basic で。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.

を、要素自体の値によって、シーケンスを順序付けるに identity 関数を指定します (x => x Visual C# またはFunction(x) xVisual Basic) の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.

このメソッドの例は、次を参照してください。OrderByDescending<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IComparer<TKey>)します。For an example of this method, see OrderByDescending<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IComparer<TKey>).

型を拡張する 2 つのメソッドが定義されているIOrderedEnumerable<TElement>、これは、このメソッドの戻り値の型。Two methods are defined to extend the type IOrderedEnumerable<TElement>, which is the return type of this method. これら 2 つの方法では、namelyThenByThenByDescendingシーケンスを並べ替えるには、追加の並べ替え条件を指定できます。These two methods, namely ThenBy and ThenByDescending, enable you to specify additional sort criteria to sort a sequence. ThenBy ThenByDescendingを返すことも、 IOrderedEnumerable<TElement>、つまり、任意の数を連続して呼び出すのThenByまたはThenByDescending行んだことができます。ThenBy and ThenByDescending also return an IOrderedEnumerable<TElement>, which means any number of consecutive calls to ThenBy or ThenByDescending can be made.

注意

IOrderedEnumerable<TElement>継承IEnumerable<T>、呼び出すことができますOrderByまたはOrderByDescendingへの呼び出しの結果にOrderByOrderByDescendingThenByまたはThenByDescendingします。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. これを行うには、新しいプライマリ順序を以前に確立された順序を無視するが導入されています。Doing this introduces a new primary ordering that ignores the previously established ordering.

このメソッドは、既定の比較子を使用してキーを比較Defaultします。This method compares keys by using the default comparer Default.

このメソッドは、安定した並べ替え; を実行します。つまり、2 つの要素のキーが等しい場合は、要素の順序が保持されます。This method performs a stable sort; that is, if the keys of two elements are equal, the order of the elements is preserved. これに対し、不安定な並べ替えは、同じキーを持つ要素の順序は保持されません。In contrast, an unstable sort does not preserve the order of elements that have the same key.

クエリ式の構文で、 orderby descending (Visual C#) またはOrder By Descendingの呼び出しに変換します (Visual Basic) 句OrderByDescendingします。In query expression syntax, an orderby descending (Visual C#) or Order By Descending (Visual Basic) clause translates to an invocation of OrderByDescending.

こちらもご覧ください

適用対象