Enumerable.ToLookup 方法

定義

Lookup<TKey,TElement> 建立泛型 IEnumerable<T>Creates a generic Lookup<TKey,TElement> from an 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>Creates a Lookup<TKey,TElement> from an IEnumerable<T> according to specified key selector and element selector functions.

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>Creates a Lookup<TKey,TElement> from an IEnumerable<T> according to a specified key selector function, a comparer and an element selector function.

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>Creates a Lookup<TKey,TElement> from an IEnumerable<T> according to a specified key selector function.

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>Creates a Lookup<TKey,TElement> from an IEnumerable<T> according to a specified key selector function and key comparer.

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>Creates a Lookup<TKey,TElement> from an IEnumerable<T> according to specified key selector and element selector functions.

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。The type of the elements of source.

TKey

keySelector 所傳回之索引鍵的型別。The type of the key returned by keySelector.

TElement

elementSelector 所傳回值的型別。The type of the value returned by elementSelector.

參數

source
IEnumerable<TSource>

用來建立 IEnumerable<T> 的來源 Lookup<TKey,TElement>The IEnumerable<T> to create a Lookup<TKey,TElement> from.

keySelector
Func<TSource,TKey>

用來從各個項目擷取索引鍵的函式。A function to extract a key from each element.

elementSelector
Func<TSource,TElement>

用來從每個項目產生結果項目值的轉換函式。A transform function to produce a result element value from each element.

傳回

ILookup<TKey,TElement>

Lookup<TKey,TElement>,包含從輸入序列選取之 TElement 類型的值。A Lookup<TKey,TElement> that contains values of type TElement selected from the input sequence.

例外狀況

sourcekeySelectorelementSelectornullsource or keySelector or elementSelector is null.

範例

下列程式碼範例示範如何使用 ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>) 來建立 Lookup<TKey,TElement>,方法是使用索引鍵選取器函式和元素選取器函數。The following code example demonstrates how to use ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>) to create a Lookup<TKey,TElement> by using a key selector function and an element selector function.

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 => Convert.ToChar(p.Company.Substring(0, 1)),
                  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

ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>) 方法會傳回一個 Lookup<TKey,TElement>,這是將索引鍵對應至值集合的一對多字典。The ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>) method returns a Lookup<TKey,TElement>, a one-to-many dictionary that maps keys to collections of values. Lookup<TKey,TElement> 不同于 Dictionary<TKey,TValue>,它會對單一值執行一對一對應的索引鍵。A Lookup<TKey,TElement> differs from a Dictionary<TKey,TValue>, which performs a one-to-one mapping of keys to single values.

預設的相等比較子 Default 用來比較索引鍵。The default equality comparer Default is used to compare keys.

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>Creates a Lookup<TKey,TElement> from an IEnumerable<T> according to a specified key selector function, a comparer and an element selector function.

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);
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。The type of the elements of source.

TKey

keySelector 所傳回之索引鍵的型別。The type of the key returned by keySelector.

TElement

elementSelector 所傳回值的型別。The type of the value returned by elementSelector.

參數

source
IEnumerable<TSource>

用來建立 IEnumerable<T> 的來源 Lookup<TKey,TElement>The IEnumerable<T> to create a Lookup<TKey,TElement> from.

keySelector
Func<TSource,TKey>

用來從各個項目擷取索引鍵的函式。A function to extract a key from each element.

elementSelector
Func<TSource,TElement>

用來從每個項目產生結果項目值的轉換函式。A transform function to produce a result element value from each element.

comparer
IEqualityComparer<TKey>

用來比較金鑰的 IEqualityComparer<T>An IEqualityComparer<T> to compare keys.

傳回

ILookup<TKey,TElement>

Lookup<TKey,TElement>,包含從輸入序列選取之 TElement 類型的值。A Lookup<TKey,TElement> that contains values of type TElement selected from the input sequence.

例外狀況

sourcekeySelectorelementSelectornullsource or keySelector or elementSelector is null.

備註

ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, IEqualityComparer<TKey>) 方法會傳回一個 Lookup<TKey,TElement>,這是將索引鍵對應至值集合的一對多字典。The ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, IEqualityComparer<TKey>) method returns a Lookup<TKey,TElement>, a one-to-many dictionary that maps keys to collections of values. Lookup<TKey,TElement> 不同于 Dictionary<TKey,TValue>,它會對單一值執行一對一對應的索引鍵。A Lookup<TKey,TElement> differs from a Dictionary<TKey,TValue>, which performs a one-to-one mapping of keys to single values.

如果 null``comparer,則會使用預設的相等比較子 Default 來比較索引鍵。If comparer is null, the default equality comparer Default is used to compare keys.

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>Creates a Lookup<TKey,TElement> from an IEnumerable<T> according to a specified key selector function.

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。The type of the elements of source.

TKey

keySelector 所傳回之索引鍵的型別。The type of the key returned by keySelector.

參數

source
IEnumerable<TSource>

用來建立 IEnumerable<T> 的來源 Lookup<TKey,TElement>The IEnumerable<T> to create a Lookup<TKey,TElement> from.

keySelector
Func<TSource,TKey>

用來從各個項目擷取索引鍵的函式。A function to extract a key from each element.

傳回

ILookup<TKey,TSource>

包含索引鍵和值的 Lookup<TKey,TElement>A Lookup<TKey,TElement> that contains keys and values. 每個群組中的值與 source 中的順序相同。The values within each group are in the same order as in source.

例外狀況

sourcekeySelectornullsource or keySelector is null.

備註

ToLookup<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>) 方法會傳回一個 Lookup<TKey,TElement>,這是將索引鍵對應至值集合的一對多字典。The ToLookup<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>) method returns a Lookup<TKey,TElement>, a one-to-many dictionary that maps keys to collections of values. Lookup<TKey,TElement> 不同于 Dictionary<TKey,TValue>,它會對單一值執行一對一對應的索引鍵。A Lookup<TKey,TElement> differs from a Dictionary<TKey,TValue>, which performs a one-to-one mapping of keys to single values.

預設的相等比較子 Default 用來比較索引鍵。The default equality comparer Default is used to compare keys.

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>Creates a Lookup<TKey,TElement> from an IEnumerable<T> according to a specified key selector function and key comparer.

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);
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。The type of the elements of source.

TKey

keySelector 所傳回之索引鍵的型別。The type of the key returned by keySelector.

參數

source
IEnumerable<TSource>

用來建立 IEnumerable<T> 的來源 Lookup<TKey,TElement>The IEnumerable<T> to create a Lookup<TKey,TElement> from.

keySelector
Func<TSource,TKey>

用來從各個項目擷取索引鍵的函式。A function to extract a key from each element.

comparer
IEqualityComparer<TKey>

用來比較金鑰的 IEqualityComparer<T>An IEqualityComparer<T> to compare keys.

傳回

ILookup<TKey,TSource>

包含索引鍵和值的 Lookup<TKey,TElement>A Lookup<TKey,TElement> that contains keys and values. 每個群組中的值與 source 中的順序相同。The values within each group are in the same order as in source.

例外狀況

sourcekeySelectornullsource or keySelector is null.

備註

ToLookup<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IEqualityComparer<TKey>) 方法會傳回一個 Lookup<TKey,TElement>,這是將索引鍵對應至值集合的一對多字典。The ToLookup<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IEqualityComparer<TKey>) method returns a Lookup<TKey,TElement>, a one-to-many dictionary that maps keys to collections of values. Lookup<TKey,TElement> 不同于 Dictionary<TKey,TValue>,它會對單一值執行一對一對應的索引鍵。A Lookup<TKey,TElement> is different to a Dictionary<TKey,TValue>, which performs a one-to-one mapping of keys to single values.

如果 null``comparer,則會使用預設的相等比較子 Default 來比較索引鍵。If comparer is null, the default equality comparer Default is used to compare keys.

適用於