Enumerable.ToLookup 方法

定义

IEnumerable<T> 生成一个泛型 Lookup<TKey,TElement>Creates a generic Lookup<TKey,TElement> from an IEnumerable<T>.

重载

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

根据指定的键选择器和元素选择器函数,从 IEnumerable<T> 创建一个 Lookup<TKey,TElement>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>)

根据指定的键选择器函数、比较器和元素选择器函数,从 IEnumerable<T> 创建一个 Lookup<TKey,TElement>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>)

根据指定的键选择器函数,从 IEnumerable<T> 创建一个 Lookup<TKey,TElement>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>)

根据指定的键选择器函数和键比较器,从 IEnumerable<T> 创建一个 Lookup<TKey,TElement>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>)

根据指定的键选择器和元素选择器函数,从 IEnumerable<T> 创建一个 Lookup<TKey,TElement>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)

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.

TElement

elementSelector 返回的值的类型。The type of the value returned by elementSelector.

参数

source
IEnumerable<TSource>

要从其创建 Lookup<TKey,TElement>IEnumerable<T>The IEnumerable<T> to create a Lookup<TKey,TElement> from.

keySelector
Func<TSource,TKey>

用于从每个元素中提取键的函数。A function to extract a key from each element.

elementSelector
Func<TSource,TElement>

用于从每个元素产生结果元素值的转换函数。A transform function to produce a result element value from each element.

返回

一个包含从输入序列中选择的类型为 TElement 的值的 Lookup<TKey,TElement>A Lookup<TKey,TElement> that contains values of type TElement selected from the input sequence.

例外

sourcekeySelectorelementSelectornullsource or keySelector or elementSelector is null.

示例

下面的代码示例演示如何使用 ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>) 通过键选择器函数和元素选择器函数创建 Lookup<TKey,TElement>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

注解

ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>) 方法返回一个 Lookup<TKey,TElement>,这是一个一对多的字典,该字典将键映射到值的集合。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>Dictionary<TKey,TValue>不同,后者执行键到单个值的一对一映射。A Lookup<TKey,TElement> differs from a Dictionary<TKey,TValue>, which performs a one-to-one mapping of keys to single values.

使用默认的相等比较器 Default 来比较键。The default equality comparer Default is used to compare keys.

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

根据指定的键选择器函数、比较器和元素选择器函数,从 IEnumerable<T> 创建一个 Lookup<TKey,TElement>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)

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.

TElement

elementSelector 返回的值的类型。The type of the value returned by elementSelector.

参数

source
IEnumerable<TSource>

要从其创建 Lookup<TKey,TElement>IEnumerable<T>The IEnumerable<T> to create a Lookup<TKey,TElement> from.

keySelector
Func<TSource,TKey>

用于从每个元素中提取键的函数。A function to extract a key from each element.

elementSelector
Func<TSource,TElement>

用于从每个元素产生结果元素值的转换函数。A transform function to produce a result element value from each element.

comparer
IEqualityComparer<TKey>

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

返回

一个包含从输入序列中选择的类型为 TElement 的值的 Lookup<TKey,TElement>A Lookup<TKey,TElement> that contains values of type TElement selected from the input sequence.

例外

sourcekeySelectorelementSelectornullsource or keySelector or elementSelector is null.

注解

ToLookup<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, IEqualityComparer<TKey>) 方法返回一个 Lookup<TKey,TElement>,这是一个一对多的字典,该字典将键映射到值的集合。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>Dictionary<TKey,TValue>不同,后者执行键到单个值的一对一映射。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,则使用默认的相等比较器 Default 来比较键。If comparer is null, the default equality comparer Default is used to compare keys.

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

根据指定的键选择器函数,从 IEnumerable<T> 创建一个 Lookup<TKey,TElement>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)

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>

要从其创建 Lookup<TKey,TElement>IEnumerable<T>The IEnumerable<T> to create a Lookup<TKey,TElement> from.

keySelector
Func<TSource,TKey>

用于从每个元素中提取键的函数。A function to extract a key from each element.

返回

ILookup<TKey,TSource>

一个包含键和值的 Lookup<TKey,TElement>A Lookup<TKey,TElement> that contains keys and values.

例外

sourcekeySelectornullsource or keySelector is null.

注解

ToLookup<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>) 方法返回一个 Lookup<TKey,TElement>,这是一个一对多的字典,该字典将键映射到值的集合。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>Dictionary<TKey,TValue>不同,后者执行键到单个值的一对一映射。A Lookup<TKey,TElement> differs from a Dictionary<TKey,TValue>, which performs a one-to-one mapping of keys to single values.

使用默认的相等比较器 Default 来比较键。The default equality comparer Default is used to compare keys.

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

根据指定的键选择器函数和键比较器,从 IEnumerable<T> 创建一个 Lookup<TKey,TElement>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)

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>

要从其创建 Lookup<TKey,TElement>IEnumerable<T>The IEnumerable<T> to create a Lookup<TKey,TElement> from.

keySelector
Func<TSource,TKey>

用于从每个元素中提取键的函数。A function to extract a key from each element.

comparer
IEqualityComparer<TKey>

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

返回

ILookup<TKey,TSource>

一个包含键和值的 Lookup<TKey,TElement>A Lookup<TKey,TElement> that contains keys and values.

例外

sourcekeySelectornullsource or keySelector is null.

注解

ToLookup<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IEqualityComparer<TKey>) 方法返回一个 Lookup<TKey,TElement>,这是一个一对多的字典,该字典将键映射到值的集合。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>Dictionary<TKey,TValue>不同,后者执行键到单个值的一对一映射。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,则使用默认的相等比较器 Default 来比较键。If comparer is null, the default equality comparer Default is used to compare keys.

适用于