Enumerable.ToLookup 方法
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>。
- 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
Lookup<TKey,TElement>，包含從輸入序列選取之 TElement 類型的值。
例外狀況
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
.NET 9 和其他版本
| 產品 | 版本 |
|---|---|
| .NET | Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9 |
| .NET Framework | 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
| .NET Standard | 1.0, 1.1, 1.2, 1.3, 1.4, 1.6, 2.0, 2.1 |
| UWP | 10.0 |
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
Lookup<TKey,TElement>，包含從輸入序列選取之 TElement 類型的值。
例外狀況
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
.NET 9 和其他版本
| 產品 | 版本 |
|---|---|
| .NET | Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9 |
| .NET Framework | 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
| .NET Standard | 1.0, 1.1, 1.2, 1.3, 1.4, 1.6, 2.0, 2.1 |
| UWP | 10.0 |
- 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
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
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
.NET 9 和其他版本
| 產品 | 版本 |
|---|---|
| .NET | Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9 |
| .NET Framework | 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
| .NET Standard | 1.0, 1.1, 1.2, 1.3, 1.4, 1.6, 2.0, 2.1 |
| UWP | 10.0 |
- 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
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
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
.NET 9 和其他版本
| 產品 | 版本 |
|---|---|
| .NET | Core 1.0, Core 1.1, Core 2.0, Core 2.1, Core 2.2, Core 3.0, Core 3.1, 5, 6, 7, 8, 9 |
| .NET Framework | 3.5, 4.0, 4.5, 4.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, 4.8, 4.8.1 |
| .NET Standard | 1.0, 1.1, 1.2, 1.3, 1.4, 1.6, 2.0, 2.1 |
| UWP | 10.0 |
