Enumerable.ToLookup 方法

參考

定義

命名空間:: System.Linq

組件:: System.Linq.dll

組件:: System.Core.dll

組件:: netstandard.dll

重要

部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。

從 Lookup<TKey,TElement> 建立泛型 IEnumerable<T>。

多載

ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>)	根據指定的索引鍵選取器和項目選取器函式，從 Lookup<TKey,TElement> 建立 IEnumerable<T>。
ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, IEqualityComparer<TKey>)	根據指定的索引鍵選取器函式、比較子和項目選取器函式，從 Lookup<TKey,TElement> 建立 IEnumerable<T>。
ToLookup<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IEqualityComparer<TKey>)	根據指定的索引鍵選取器函式和索引鍵比較子，從 Lookup<TKey,TElement> 建立 IEnumerable<T>。
ToLookup<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>)	根據指定的索引鍵選擇器函式，從 Lookup<TKey,TElement> 建立 IEnumerable<T>。

ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>)

來源:: Lookup.cs

來源:: Lookup.cs

來源:: Lookup.cs

根據指定的索引鍵選取器和項目選取器函式，從 Lookup<TKey,TElement> 建立 IEnumerable<T>。

public:
generic <typename TSource, typename TKey, typename TElement>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::ILookup<TKey, TElement> ^ ToLookup(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector, Func<TSource, TElement> ^ elementSelector);

public static System.Linq.ILookup<TKey,TElement> ToLookup<TSource,TKey,TElement> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, Func<TSource,TElement> elementSelector);

static member ToLookup : seq<'Source> * Func<'Source, 'Key> * Func<'Source, 'Element> -> System.Linq.ILookup<'Key, 'Element>

<Extension()>
Public Function ToLookup(Of TSource, TKey, TElement) (source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey), elementSelector As Func(Of TSource, TElement)) As ILookup(Of TKey, TElement)

類型參數

TSource

source 項目的類型。

TKey

keySelector 所傳回之索引鍵的型別。

TElement

elementSelector 所傳回值的型別。

參數

source: IEnumerable<TSource>

用來建立 IEnumerable<T> 的來源 Lookup<TKey,TElement>。

keySelector: Func<TSource,TKey>

用來從各個項目擷取索引鍵的函式。

elementSelector: Func<TSource,TElement>

用來從每個項目產生結果項目值的轉換函式。

傳回

ILookup<TKey,TElement>

Lookup<TKey,TElement>，包含從輸入序列選取之 TElement 類型的值。

例外狀況

ArgumentNullException

source、keySelector 或 elementSelector 為 null。

範例

下列程式代碼範例示範如何使用 ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>) 索引鍵選取器函式和項目選取器函式來建立 Lookup<TKey,TElement> 。

class Package
{
    public string Company { get; set; }
    public double Weight { get; set; }
    public long TrackingNumber { get; set; }
}

public static void ToLookupEx1()
{
    // Create a list of Packages.
    List<Package> packages =
        new List<Package>
            { new Package { Company = "Coho Vineyard",
                  Weight = 25.2, TrackingNumber = 89453312L },
              new Package { Company = "Lucerne Publishing",
                  Weight = 18.7, TrackingNumber = 89112755L },
              new Package { Company = "Wingtip Toys",
                  Weight = 6.0, TrackingNumber = 299456122L },
              new Package { Company = "Contoso Pharmaceuticals",
                  Weight = 9.3, TrackingNumber = 670053128L },
              new Package { Company = "Wide World Importers",
                  Weight = 33.8, TrackingNumber = 4665518773L } };

    // Create a Lookup to organize the packages.
    // Use the first character of Company as the key value.
    // Select Company appended to TrackingNumber
    // as the element values of the Lookup.
    ILookup<char, string> lookup =
        packages
        .ToLookup(p => p.Company[0],
                  p => p.Company + " " + p.TrackingNumber);

    // Iterate through each IGrouping in the Lookup.
    foreach (IGrouping<char, string> packageGroup in lookup)
    {
        // Print the key value of the IGrouping.
        Console.WriteLine(packageGroup.Key);
        // Iterate through each value in the
        // IGrouping and print its value.
        foreach (string str in packageGroup)
            Console.WriteLine("    {0}", str);
    }
}

/*
 This code produces the following output:

 C
     Coho Vineyard 89453312
     Contoso Pharmaceuticals 670053128
 L
     Lucerne Publishing 89112755
 W
     Wingtip Toys 299456122
     Wide World Importers 4665518773
*/

Structure Package
    Public Company As String
    Public Weight As Double
    Public TrackingNumber As Long
End Structure

Sub ToLookupEx1()
    ' Create a list of Packages.
    Dim packages As New List(Of Package)(New Package() _
     {New Package With
      {.Company = "Coho Vineyard", .Weight = 25.2, .TrackingNumber = 89453312L},
      New Package With
      {.Company = "Lucerne Publishing", .Weight = 18.7, .TrackingNumber = 89112755L},
      New Package With
      {.Company = "Wingtip Toys", .Weight = 6.0, .TrackingNumber = 299456122L},
      New Package With
      {.Company = "Contoso Pharmaceuticals", .Weight = 9.3, .TrackingNumber = 670053128L},
      New Package With
      {.Company = "Wide World Importers", .Weight = 33.8, .TrackingNumber = 4665518773L}})

    ' Create a Lookup to organize the packages.
    ' Use the first character of Company as the key value.
    ' Select Company appended to TrackingNumber
    ' as the element values of the Lookup.
    Dim lookup As ILookup(Of Char, String) =
    packages.ToLookup(Function(p) _
                          Convert.ToChar(p.Company.Substring(0, 1)),
                      Function(p) _
                          p.Company & " " & p.TrackingNumber)

    Dim output As New System.Text.StringBuilder

    ' Iterate through each IGrouping in the Lookup.
    For Each packageGroup As IGrouping(Of Char, String) In lookup
        ' Print the key value of the IGrouping.
        output.AppendLine(packageGroup.Key)
        ' Iterate through each value in the IGrouping and print its value.
        For Each str As String In packageGroup
            output.AppendLine("   " & str)
        Next
    Next

    ' Select a group of packages by indexing directly into the Lookup.
    Dim cgroup As IEnumerable(Of String) = lookup("C"c)

    output.AppendLine(vbCrLf & "Packages from Company names that start with 'C':")
    For Each str As String In cgroup
        output.AppendLine(str)
    Next

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

' This code produces the following output:
'
' C
'    Coho Vineyard 89453312
'    Contoso Pharmaceuticals 670053128
' L
'    Lucerne Publishing 89112755
' W
'    Wingtip Toys 299456122
'    Wide World Importers 4665518773
'
' Packages from Company names that start with 'C':
' Coho Vineyard 89453312
' Contoso Pharmaceuticals 670053128

備註

方法會 ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>) 傳 Lookup<TKey,TElement>回，這是一對多字典，可將索引鍵對應至值的集合。不同於 Dictionary<TKey,TValue>，Lookup<TKey,TElement>它會執行索引鍵與單一值的一對一對應。

默認相等比較子 Default 是用來比較索引鍵。

適用於

ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, IEqualityComparer<TKey>)

來源:: Lookup.cs

來源:: Lookup.cs

來源:: Lookup.cs

根據指定的索引鍵選取器函式、比較子和項目選取器函式，從 Lookup<TKey,TElement> 建立 IEnumerable<T>。

public:
generic <typename TSource, typename TKey, typename TElement>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::ILookup<TKey, TElement> ^ ToLookup(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector, Func<TSource, TElement> ^ elementSelector, System::Collections::Generic::IEqualityComparer<TKey> ^ comparer);

public static System.Linq.ILookup<TKey,TElement> ToLookup<TSource,TKey,TElement> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, Func<TSource,TElement> elementSelector, System.Collections.Generic.IEqualityComparer<TKey> comparer);

public static System.Linq.ILookup<TKey,TElement> ToLookup<TSource,TKey,TElement> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, Func<TSource,TElement> elementSelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer);

static member ToLookup : seq<'Source> * Func<'Source, 'Key> * Func<'Source, 'Element> * System.Collections.Generic.IEqualityComparer<'Key> -> System.Linq.ILookup<'Key, 'Element>

<Extension()>
Public Function ToLookup(Of TSource, TKey, TElement) (source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey), elementSelector As Func(Of TSource, TElement), comparer As IEqualityComparer(Of TKey)) As ILookup(Of TKey, TElement)

類型參數

TSource

source 項目的類型。

TKey

keySelector 所傳回之索引鍵的型別。

TElement

elementSelector 所傳回值的型別。

參數

source: IEnumerable<TSource>

用來建立 IEnumerable<T> 的來源 Lookup<TKey,TElement>。

keySelector: Func<TSource,TKey>

用來從各個項目擷取索引鍵的函式。

elementSelector: Func<TSource,TElement>

用來從每個項目產生結果項目值的轉換函式。

comparer: IEqualityComparer<TKey>

用來比較金鑰的 IEqualityComparer<T>。

傳回

ILookup<TKey,TElement>

Lookup<TKey,TElement>，包含從輸入序列選取之 TElement 類型的值。

例外狀況

ArgumentNullException

source、keySelector 或 elementSelector 為 null。

備註

方法會 ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, IEqualityComparer<TKey>) 傳 Lookup<TKey,TElement>回，這是一對多字典，可將索引鍵對應至值的集合。不同於 Dictionary<TKey,TValue>，Lookup<TKey,TElement>它會執行索引鍵與單一值的一對一對應。

如果為 comparernull，則會使用預設相等比較子 Default 來比較索引鍵。

適用於

ToLookup<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IEqualityComparer<TKey>)

來源:: Lookup.cs

來源:: Lookup.cs

來源:: Lookup.cs

根據指定的索引鍵選取器函式和索引鍵比較子，從 Lookup<TKey,TElement> 建立 IEnumerable<T>。

public:
generic <typename TSource, typename TKey>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::ILookup<TKey, TSource> ^ ToLookup(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector, System::Collections::Generic::IEqualityComparer<TKey> ^ comparer);

public static System.Linq.ILookup<TKey,TSource> ToLookup<TSource,TKey> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, System.Collections.Generic.IEqualityComparer<TKey> comparer);

public static System.Linq.ILookup<TKey,TSource> ToLookup<TSource,TKey> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, System.Collections.Generic.IEqualityComparer<TKey>? comparer);

static member ToLookup : seq<'Source> * Func<'Source, 'Key> * System.Collections.Generic.IEqualityComparer<'Key> -> System.Linq.ILookup<'Key, 'Source>

<Extension()>
Public Function ToLookup(Of TSource, TKey) (source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey), comparer As IEqualityComparer(Of TKey)) As ILookup(Of TKey, TSource)

類型參數

TSource

source 項目的類型。

TKey

keySelector 所傳回之索引鍵的型別。

參數

source: IEnumerable<TSource>

用來建立 IEnumerable<T> 的來源 Lookup<TKey,TElement>。

keySelector: Func<TSource,TKey>

用來從各個項目擷取索引鍵的函式。

comparer: IEqualityComparer<TKey>

用來比較金鑰的 IEqualityComparer<T>。

傳回

ILookup<TKey,TSource>

包含索引鍵和值的 Lookup<TKey,TElement>。每個群組中的值與 source 中的順序相同。

例外狀況

ArgumentNullException

source 或 keySelector 為 null。

備註

方法會 ToLookup<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IEqualityComparer<TKey>) 傳 Lookup<TKey,TElement>回，這是一對多字典，可將索引鍵對應至值的集合。 Lookup<TKey,TElement>與不同Dictionary<TKey,TValue>，它會執行索引鍵與單一值的一對一對應。

如果為 comparernull，則會使用預設相等比較子 Default 來比較索引鍵。

適用於

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

來源:: Lookup.cs

來源:: Lookup.cs

來源:: Lookup.cs

根據指定的索引鍵選擇器函式，從 Lookup<TKey,TElement> 建立 IEnumerable<T>。

public:
generic <typename TSource, typename TKey>
[System::Runtime::CompilerServices::Extension]
 static System::Linq::ILookup<TKey, TSource> ^ ToLookup(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector);

public static System.Linq.ILookup<TKey,TSource> ToLookup<TSource,TKey> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector);

static member ToLookup : seq<'Source> * Func<'Source, 'Key> -> System.Linq.ILookup<'Key, 'Source>

<Extension()>
Public Function ToLookup(Of TSource, TKey) (source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey)) As ILookup(Of TKey, TSource)

類型參數

TSource

source 項目的類型。

TKey

keySelector 所傳回之索引鍵的型別。

參數

source: IEnumerable<TSource>

用來建立 IEnumerable<T> 的來源 Lookup<TKey,TElement>。

keySelector: Func<TSource,TKey>

用來從各個項目擷取索引鍵的函式。

傳回

ILookup<TKey,TSource>

包含索引鍵和值的 Lookup<TKey,TElement>。每個群組中的值與 source 中的順序相同。

例外狀況

ArgumentNullException

source 或 keySelector 為 null。

備註

方法會 ToLookup<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>) 傳 Lookup<TKey,TElement>回，這是一對多字典，可將索引鍵對應至值的集合。不同於 Dictionary<TKey,TValue>，Lookup<TKey,TElement>它會執行索引鍵與單一值的一對一對應。

默認相等比較子 Default 是用來比較索引鍵。

適用於

共用方式為

Enumerable.ToLookup 方法

定義

多載

ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>)

類型參數

參數

傳回

例外狀況

範例

備註

適用於

ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, IEqualityComparer<TKey>)

類型參數

參數

傳回

例外狀況

備註

適用於

ToLookup<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IEqualityComparer<TKey>)

類型參數

參數

傳回

例外狀況

備註

適用於

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

類型參數

參數

傳回

例外狀況

備註

適用於

其他資源