Enumerable.GroupBy Enumerable.GroupBy Enumerable.GroupBy Enumerable.GroupBy Method

定義

群組序列的項目。Groups the elements of a sequence.

多載

GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>,TResult>) GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>,TResult>) GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>,TResult>) GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>,TResult>)

依據指定的索引鍵選取器函式來群組序列的項目,並從每個群組及其索引鍵建立結果值。Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. 每個群組的項目都是利用指定的函式進行投影。The elements of each group are projected by using a specified function.

GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>,TResult>, IEqualityComparer<TKey>) GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>,TResult>, IEqualityComparer<TKey>) GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>,TResult>, IEqualityComparer<TKey>) GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>,TResult>, IEqualityComparer<TKey>)

依據指定的索引鍵選取器函式來群組序列的項目,並從每個群組及其索引鍵建立結果值。Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. 索引鍵值是使用指定的比較子來進行比較,而每個群組的項目則都是利用指定的函式進行投影。Key values are compared by using a specified comparer, and the elements of each group are projected by using a specified function.

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

群組根據指定的索引鍵選取器函式,以及專案使用指定的函式的每個群組的項目序列的項目。Groups the elements of a sequence according to a specified key selector function and projects the elements for each group by using a specified function.

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

群組依據索引鍵選取器函式序列的項目。Groups the elements of a sequence according to a key selector function. 索引鍵是使用比較子來進行比較,而每個群組的項目都是利用指定的函式進行投影。The keys are compared by using a comparer and each group's elements are projected by using a specified function.

GroupBy<TSource,TKey,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TKey,IEnumerable<TSource>,TResult>) GroupBy<TSource,TKey,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TKey,IEnumerable<TSource>,TResult>) GroupBy<TSource,TKey,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TKey,IEnumerable<TSource>,TResult>) GroupBy<TSource,TKey,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TKey,IEnumerable<TSource>,TResult>)

依據指定的索引鍵選取器函式來群組序列的項目,並從每個群組及其索引鍵建立結果值。Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key.

GroupBy<TSource,TKey,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TKey,IEnumerable<TSource>,TResult>, IEqualityComparer<TKey>) GroupBy<TSource,TKey,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TKey,IEnumerable<TSource>,TResult>, IEqualityComparer<TKey>) GroupBy<TSource,TKey,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TKey,IEnumerable<TSource>,TResult>, IEqualityComparer<TKey>) GroupBy<TSource,TKey,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TKey,IEnumerable<TSource>,TResult>, IEqualityComparer<TKey>)

依據指定的索引鍵選取器函式來群組序列的項目,並從每個群組及其索引鍵建立結果值。Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. 索引鍵是使用指定的比較子來進行比較。The keys are compared by using a specified comparer.

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

分組依據指定的索引鍵選取器函式序列的項目。Groups the elements of a sequence according to a specified key selector function.

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

群組的順序,根據指定的索引鍵選取器函式和比較使用指定的比較子索引鍵的項目。Groups the elements of a sequence according to a specified key selector function and compares the keys by using a specified comparer.

GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>,TResult>) GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>,TResult>) GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>,TResult>) GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>,TResult>)

依據指定的索引鍵選取器函式來群組序列的項目,並從每個群組及其索引鍵建立結果值。Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. 每個群組的項目都是利用指定的函式進行投影。The elements of each group are projected by using a specified function.

public:
generic <typename TSource, typename TKey, typename TElement, typename TResult>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::IEnumerable<TResult> ^ GroupBy(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector, Func<TSource, TElement> ^ elementSelector, Func<TKey, System::Collections::Generic::IEnumerable<TElement> ^, TResult> ^ resultSelector);
public static System.Collections.Generic.IEnumerable<TResult> GroupBy<TSource,TKey,TElement,TResult> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, Func<TSource,TElement> elementSelector, Func<TKey,System.Collections.Generic.IEnumerable<TElement>,TResult> resultSelector);
static member GroupBy : seq<'Source> * Func<'Source, 'Key> * Func<'Source, 'Element> * Func<'Key, seq<'Element>, 'Result> -> seq<'Result>
<Extension()>
Public Function GroupBy(Of TSource, TKey, TElement, TResult) (source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey), elementSelector As Func(Of TSource, TElement), resultSelector As Func(Of TKey, IEnumerable(Of TElement), TResult)) As IEnumerable(Of TResult)

類型參數

TSource

source 項目的類型。The type of the elements of source.

TKey

所傳回的索引鍵類型keySelectorThe type of the key returned by keySelector.

TElement

在每個元素的型別IGrouping<TKey,TElement>The type of the elements in each IGrouping<TKey,TElement>.

TResult

所傳回之結果值的型別resultSelectorThe type of the result value returned by resultSelector.

參數

source
IEnumerable<TSource>

IEnumerable<T>群組其項目。An IEnumerable<T> whose elements to group.

keySelector
Func<TSource,TKey>

用來擷取各項目之索引鍵的函式。A function to extract the key for each element.

elementSelector
Func<TSource,TElement>

若要將每個來源項目對應中的項目函式IGrouping<TKey,TElement>A function to map each source element to an element in an IGrouping<TKey,TElement>.

resultSelector
Func<TKey,IEnumerable<TElement>,TResult>

用來從各個群組建立結果值的函式。A function to create a result value from each group.

傳回

IEnumerable<TResult>

型別的項目集合TResult其中每個項目代表投影的群組和其索引鍵。A collection of elements of type TResult where each element represents a projection over a group and its key.

範例

下列程式碼範例示範如何使用GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>,TResult>)分組序列的預測的項目,並接著按一下 專案類型的結果的序列TResultThe following code example demonstrates how to use GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>,TResult>) to group the projected elements of a sequence and then project a sequence of results of type TResult.

class Pet
{
    public string Name { get; set; }
    public double Age { get; set; }
}

public static void GroupByEx4()
{
    // Create a list of pets.
    List<Pet> petsList =
        new List<Pet>{ new Pet { Name="Barley", Age=8.3 },
                       new Pet { Name="Boots", Age=4.9 },
                       new Pet { Name="Whiskers", Age=1.5 },
                       new Pet { Name="Daisy", Age=4.3 } };

    // Group Pet.Age values by the Math.Floor of the age.
    // Then project an anonymous type from each group
    // that consists of the key, the count of the group's
    // elements, and the minimum and maximum age in the group.
    var query = petsList.GroupBy(
        pet => Math.Floor(pet.Age),
        pet => pet.Age,
        (baseAge, ages) => new
        {
            Key = baseAge,
            Count = ages.Count(),
            Min = ages.Min(),
            Max = ages.Max()
        });

    // Iterate over each anonymous type.
    foreach (var result in query)
    {
        Console.WriteLine("\nAge group: " + result.Key);
        Console.WriteLine("Number of pets in this age group: " + result.Count);
        Console.WriteLine("Minimum age: " + result.Min);
        Console.WriteLine("Maximum age: " + result.Max);
    }

    /*  This code produces the following output:
     
        Age group: 8
        Number of pets in this age group: 1
        Minimum age: 8.3
        Maximum age: 8.3
     
        Age group: 4
        Number of pets in this age group: 2
        Minimum age: 4.3
        Maximum age: 4.9
     
        Age group: 1
        Number of pets in this age group: 1
        Minimum age: 1.5
        Maximum age: 1.5
    */
}
Structure Pet
    Public Name As String
    Public Age As Double
End Structure

Public Sub GroupByEx4()
    ' Create a list of pets.
    Dim petsList As New List(Of Pet)(New Pet() _
                         {New Pet With {.Name = "Barley", .Age = 8.3},
                          New Pet With {.Name = "Boots", .Age = 4.9},
                          New Pet With {.Name = "Whiskers", .Age = 1.5},
                          New Pet With {.Name = "Daisy", .Age = 4.3}})

    ' Group Pet.Age values by the Math.Floor of the age.
    ' Then project an anonymous type from each group
    ' that consists of the key, the count of the group's
    ' elements, and the minimum and maximum age in the group.
    Dim query = petsList.GroupBy(
Function(pet) Math.Floor(pet.Age),
Function(pet) pet.Age,
Function(baseAge, ages) New With
    {.Key = baseAge,
    .Count = ages.Count(),
    .Min = ages.Min(),
    .Max = ages.Max()}
)

    Dim output As New System.Text.StringBuilder
    ' Iterate over each anonymous type.
    For Each result In query
        output.AppendLine(vbCrLf & "Age group: " & result.Key)
        output.AppendLine("Number of pets in this age group: " & result.Count)
        output.AppendLine("Minimum age: " & result.Min)
        output.AppendLine("Maximum age: " & result.Max)
    Next

    ' Display the output.
    MsgBox(output.ToString)
End Sub

' This code produces the following output:

' Age group: 8
' Number of pets in this age group: 1
' Minimum age: 8.3
' Maximum age: 8.3
'
' Age group: 4
' Number of pets in this age group: 2
' Minimum age: 4.3
' Maximum age: 4.9
'
' Age group: 1
' Number of pets in this age group: 1
' Minimum age: 1.5
' Maximum age: 1.5

備註

在查詢運算式語法中, group by (Visual C#) 或Group By Into(Visual Basic) 子句會轉譯成的引動過程GroupByIn query expression syntax, a group by (Visual C#) or Group By Into (Visual Basic) clause translates to an invocation of GroupBy.

另請參閱

GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>,TResult>, IEqualityComparer<TKey>) GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>,TResult>, IEqualityComparer<TKey>) GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>,TResult>, IEqualityComparer<TKey>) GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>,TResult>, IEqualityComparer<TKey>)

依據指定的索引鍵選取器函式來群組序列的項目,並從每個群組及其索引鍵建立結果值。Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. 索引鍵值是使用指定的比較子來進行比較,而每個群組的項目則都是利用指定的函式進行投影。Key values are compared by using a specified comparer, and the elements of each group are projected by using a specified function.

public:
generic <typename TSource, typename TKey, typename TElement, typename TResult>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::IEnumerable<TResult> ^ GroupBy(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector, Func<TSource, TElement> ^ elementSelector, Func<TKey, System::Collections::Generic::IEnumerable<TElement> ^, TResult> ^ resultSelector, System::Collections::Generic::IEqualityComparer<TKey> ^ comparer);
public static System.Collections.Generic.IEnumerable<TResult> GroupBy<TSource,TKey,TElement,TResult> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, Func<TSource,TElement> elementSelector, Func<TKey,System.Collections.Generic.IEnumerable<TElement>,TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey> comparer);
static member GroupBy : seq<'Source> * Func<'Source, 'Key> * Func<'Source, 'Element> * Func<'Key, seq<'Element>, 'Result> * System.Collections.Generic.IEqualityComparer<'Key> -> seq<'Result>
<Extension()>
Public Function GroupBy(Of TSource, TKey, TElement, TResult) (source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey), elementSelector As Func(Of TSource, TElement), resultSelector As Func(Of TKey, IEnumerable(Of TElement), TResult), comparer As IEqualityComparer(Of TKey)) As IEnumerable(Of TResult)

類型參數

TSource

source 項目的類型。The type of the elements of source.

TKey

所傳回的索引鍵類型keySelectorThe type of the key returned by keySelector.

TElement

在每個元素的型別IGrouping<TKey,TElement>The type of the elements in each IGrouping<TKey,TElement>.

TResult

所傳回之結果值的型別resultSelectorThe type of the result value returned by resultSelector.

參數

source
IEnumerable<TSource>

IEnumerable<T>群組其項目。An IEnumerable<T> whose elements to group.

keySelector
Func<TSource,TKey>

用來擷取各項目之索引鍵的函式。A function to extract the key for each element.

elementSelector
Func<TSource,TElement>

若要將每個來源項目對應中的項目函式IGrouping<TKey,TElement>A function to map each source element to an element in an IGrouping<TKey,TElement>.

resultSelector
Func<TKey,IEnumerable<TElement>,TResult>

用來從各個群組建立結果值的函式。A function to create a result value from each group.

comparer
IEqualityComparer<TKey>

IEqualityComparer<T>來比較索引鍵。An IEqualityComparer<T> to compare keys with.

傳回

IEnumerable<TResult>

型別的項目集合TResult其中每個項目代表投影的群組和其索引鍵。A collection of elements of type TResult where each element represents a projection over a group and its key.

另請參閱

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

群組根據指定的索引鍵選取器函式,以及專案使用指定的函式的每個群組的項目序列的項目。Groups the elements of a sequence according to a specified key selector function and projects the elements for each group by using a specified function.

public:
generic <typename TSource, typename TKey, typename TElement>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::IEnumerable<System::Linq::IGrouping<TKey, TElement> ^> ^ GroupBy(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector, Func<TSource, TElement> ^ elementSelector);
public static System.Collections.Generic.IEnumerable<System.Linq.IGrouping<TKey,TElement>> GroupBy<TSource,TKey,TElement> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, Func<TSource,TElement> elementSelector);
static member GroupBy : seq<'Source> * Func<'Source, 'Key> * Func<'Source, 'Element> -> seq<System.Linq.IGrouping<'Key, 'Element>>
<Extension()>
Public Function GroupBy(Of TSource, TKey, TElement) (source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey), elementSelector As Func(Of TSource, TElement)) As IEnumerable(Of IGrouping(Of TKey, TElement))

類型參數

TSource

source 項目的類型。The type of the elements of source.

TKey

所傳回的索引鍵類型keySelectorThe type of the key returned by keySelector.

TElement

IGrouping<TKey,TElement> 中的項目類型。The type of the elements in the IGrouping<TKey,TElement>.

參數

source
IEnumerable<TSource>

IEnumerable<T>群組其項目。An IEnumerable<T> whose elements to group.

keySelector
Func<TSource,TKey>

用來擷取各項目之索引鍵的函式。A function to extract the key for each element.

elementSelector
Func<TSource,TElement>

若要將每個來源項目對應中的項目函式IGrouping<TKey,TElement>A function to map each source element to an element in the IGrouping<TKey,TElement>.

傳回

IEnumerable<IGrouping<TKey,TElement>>

C# 中的 IEnumerable<IGrouping<TKey, TElement>> 或 Visual Basic 中的 IEnumerable(Of IGrouping(Of TKey, TElement)),其中每個 IGrouping<TKey,TElement> 物件包含一個 TElement 類型的物件集合和一個索引鍵。An IEnumerable<IGrouping<TKey, TElement>> in C# or IEnumerable(Of IGrouping(Of TKey, TElement)) in Visual Basic where each IGrouping<TKey,TElement> object contains a collection of objects of type TElement and a key.

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GroupBy<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>)來分組序列的項目。The following code example demonstrates how to use GroupBy<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>) to group the elements of a sequence.

class Pet
{
    public string Name { get; set; }
    public int Age { get; set; }
}

// Uses method-based query syntax.
public static void GroupByEx1()
{
    // Create a list of pets.
    List<Pet> pets =
        new List<Pet>{ new Pet { Name="Barley", Age=8 },
                       new Pet { Name="Boots", Age=4 },
                       new Pet { Name="Whiskers", Age=1 },
                       new Pet { Name="Daisy", Age=4 } };

    // Group the pets using Age as the key value 
    // and selecting only the pet's Name for each value.
    IEnumerable<IGrouping<int, string>> query =
        pets.GroupBy(pet => pet.Age, pet => pet.Name);

    // Iterate over each IGrouping in the collection.
    foreach (IGrouping<int, string> petGroup in query)
    {
        // Print the key value of the IGrouping.
        Console.WriteLine(petGroup.Key);
        // Iterate over each value in the 
        // IGrouping and print the value.
        foreach (string name in petGroup)
            Console.WriteLine("  {0}", name);
    }
}

/*
 This code produces the following output:

 8
   Barley
 4
   Boots
   Daisy
 1
   Whiskers
*/
Structure Pet
    Public Name As String
    Public Age As Integer
End Structure

Sub GroupByEx1()
    'Create a list of Pet objects.
    Dim pets As New List(Of Pet)(New Pet() _
                         {New Pet With {.Name = "Barley", .Age = 8},
                          New Pet With {.Name = "Boots", .Age = 4},
                          New Pet With {.Name = "Whiskers", .Age = 1},
                          New Pet With {.Name = "Daisy", .Age = 4}})

    ' Group the pets using Age as the key 
    ' and selecting only the pet's Name for each value.
    Dim query As IEnumerable(Of IGrouping(Of Integer, String)) =
pets.GroupBy(Function(pet) pet.Age,
             Function(pet) pet.Name)

    Dim output As New System.Text.StringBuilder
    ' Iterate over each IGrouping in the collection.
    For Each petGroup As IGrouping(Of Integer, String) In query
        ' Print the key value of the IGrouping.
        output.AppendLine(petGroup.Key)
        ' Iterate over each value in the IGrouping and print the value.
        For Each name As String In petGroup
            output.AppendLine("  " & name)
        Next
    Next

    ' Display the output.
    MsgBox(output.ToString)
End Sub

' This code produces the following output:
'
' 8
'   Barley
' 4
'   Boots
'   Daisy
' 1
'   Whiskers

在查詢運算式語法中, group by (Visual C#) 或Group By Into(Visual Basic) 子句會轉譯成的引動過程GroupByIn query expression syntax, a group by (Visual C#) or Group By Into (Visual Basic) clause translates to an invocation of GroupBy. 下列範例中的查詢運算式的轉譯相當於上述範例中的查詢。The translation of the query expression in the following example is equivalent to the query in the example above.

IEnumerable<IGrouping<int, string>> query =
    from pet in pets
    group pet.Name by pet.Age;
    Dim query =
From pet In pets
Group pet.Name By Age = pet.Age Into ageGroup = Group

注意

Visual C# 或 Visual Basic 的查詢運算式中的項目和索引鍵選取範圍的運算式中發生相反的順序中呼叫的引數位置從GroupBy<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>)方法。In a Visual C# or Visual Basic query expression, the element and key selection expressions occur in the reverse order from their argument positions in a call to the GroupBy<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>) method.

備註

實作這個方法是使用延後的執行。This method is implemented by using deferred execution. 立即傳回值是儲存,才能執行此動作的所有資訊的物件。The immediate return value is an object that stores all the information that is required to perform the action. 這個方法所表示的查詢不會執行直到列舉物件可以藉由呼叫其GetEnumerator方法直接或透過foreachVisual C# 中或For EachVisual Basic 中。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.

GroupBy<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>)方法傳回的集合IGrouping<TKey,TElement>物件,一個用於每個發現的相異索引鍵。The GroupBy<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>) method returns a collection of IGrouping<TKey,TElement> objects, one for each distinct key that was encountered. IGrouping<TKey,TElement>IEnumerable<T>也具有其項目相關聯的索引鍵。An IGrouping<TKey,TElement> is an IEnumerable<T> that also has a key associated with its elements.

IGrouping<TKey,TElement>物件產生根據順序中的項目順序source產生第一個索引鍵,每個IGrouping<TKey,TElement>The IGrouping<TKey,TElement> objects are yielded in an order based on the order of the elements in source that produced the first key of each IGrouping<TKey,TElement>. 在群組中的項目產生的順序產生它們的項目會出現在sourceElements in a grouping are yielded in the order that the elements that produced them appear in source.

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

另請參閱

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

群組依據索引鍵選取器函式序列的項目。Groups the elements of a sequence according to a key selector function. 索引鍵是使用比較子來進行比較,而每個群組的項目都是利用指定的函式進行投影。The keys are compared by using a comparer and each group's elements are projected by using a specified function.

public:
generic <typename TSource, typename TKey, typename TElement>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::IEnumerable<System::Linq::IGrouping<TKey, TElement> ^> ^ GroupBy(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector, Func<TSource, TElement> ^ elementSelector, System::Collections::Generic::IEqualityComparer<TKey> ^ comparer);
public static System.Collections.Generic.IEnumerable<System.Linq.IGrouping<TKey,TElement>> GroupBy<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 GroupBy : seq<'Source> * Func<'Source, 'Key> * Func<'Source, 'Element> * System.Collections.Generic.IEqualityComparer<'Key> -> seq<System.Linq.IGrouping<'Key, 'Element>>
<Extension()>
Public Function GroupBy(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 IEnumerable(Of IGrouping(Of TKey, TElement))

類型參數

TSource

source 項目的類型。The type of the elements of source.

TKey

所傳回的索引鍵類型keySelectorThe type of the key returned by keySelector.

TElement

IGrouping<TKey,TElement> 中的項目類型。The type of the elements in the IGrouping<TKey,TElement>.

參數

source
IEnumerable<TSource>

IEnumerable<T>群組其項目。An IEnumerable<T> whose elements to group.

keySelector
Func<TSource,TKey>

用來擷取各項目之索引鍵的函式。A function to extract the key for each element.

elementSelector
Func<TSource,TElement>

若要將每個來源項目對應中的項目函式IGrouping<TKey,TElement>A function to map each source element to an element in an IGrouping<TKey,TElement>.

comparer
IEqualityComparer<TKey>

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

傳回

IEnumerable<IGrouping<TKey,TElement>>

C# 中的 IEnumerable<IGrouping<TKey, TElement>> 或 Visual Basic 中的 IEnumerable(Of IGrouping(Of TKey, TElement)),其中每個 IGrouping<TKey,TElement> 物件包含一個 TElement 類型的物件集合和一個索引鍵。An IEnumerable<IGrouping<TKey, TElement>> in C# or IEnumerable(Of IGrouping(Of TKey, TElement)) in Visual Basic where each IGrouping<TKey,TElement> object contains a collection of objects of type TElement and a key.

例外狀況

sourcekeySelectorelementSelectornullsource or keySelector or elementSelector is null.

備註

實作這個方法是使用延後的執行。This method is implemented by using deferred execution. 立即傳回值是儲存,才能執行此動作的所有資訊的物件。The immediate return value is an object that stores all the information that is required to perform the action. 這個方法所表示的查詢不會執行直到列舉物件可以藉由呼叫其GetEnumerator方法直接或透過foreachVisual C# 中或For EachVisual Basic 中。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.

GroupBy<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, IEqualityComparer<TKey>)方法傳回的集合IGrouping<TKey,TElement>物件,一個用於每個發現的相異索引鍵。The GroupBy<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, IEqualityComparer<TKey>) method returns a collection of IGrouping<TKey,TElement> objects, one for each distinct key that was encountered. IGrouping<TKey,TElement>IEnumerable<T>也具有其項目相關聯的索引鍵。An IGrouping<TKey,TElement> is an IEnumerable<T> that also has a key associated with its elements.

IGrouping<TKey,TElement>物件產生根據順序中的項目順序source產生第一個索引鍵,每個IGrouping<TKey,TElement>The IGrouping<TKey,TElement> objects are yielded in an order based on the order of the elements in source that produced the first key of each IGrouping<TKey,TElement>. 在群組中的項目產生的順序產生它們的項目會出現在sourceElements in a grouping are yielded in the order that the elements that produced them appear in source.

如果comparernull,預設相等比較子Default用來比較索引鍵。If comparer is null, the default equality comparer Default is used to compare keys.

如果兩個金鑰會被視為相等於根據comparer,第一個索引鍵會被選為該群組的索引鍵。If two keys are considered equal according to comparer, the first key is chosen as the key for that grouping.

在查詢運算式語法中, group by (Visual C#) 或Group By Into(Visual Basic) 子句會轉譯成的引動過程GroupByIn query expression syntax, a group by (Visual C#) or Group By Into (Visual Basic) clause translates to an invocation of GroupBy. 如需詳細資訊和使用方式範例,請參閱 < group 子句By 子句群組For more information and usage examples, see group clause and Group By Clause.

另請參閱

GroupBy<TSource,TKey,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TKey,IEnumerable<TSource>,TResult>) GroupBy<TSource,TKey,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TKey,IEnumerable<TSource>,TResult>) GroupBy<TSource,TKey,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TKey,IEnumerable<TSource>,TResult>) GroupBy<TSource,TKey,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TKey,IEnumerable<TSource>,TResult>)

依據指定的索引鍵選取器函式來群組序列的項目,並從每個群組及其索引鍵建立結果值。Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key.

public:
generic <typename TSource, typename TKey, typename TResult>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::IEnumerable<TResult> ^ GroupBy(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector, Func<TKey, System::Collections::Generic::IEnumerable<TSource> ^, TResult> ^ resultSelector);
public static System.Collections.Generic.IEnumerable<TResult> GroupBy<TSource,TKey,TResult> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, Func<TKey,System.Collections.Generic.IEnumerable<TSource>,TResult> resultSelector);
static member GroupBy : seq<'Source> * Func<'Source, 'Key> * Func<'Key, seq<'Source>, 'Result> -> seq<'Result>
<Extension()>
Public Function GroupBy(Of TSource, TKey, TResult) (source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey), resultSelector As Func(Of TKey, IEnumerable(Of TSource), TResult)) As IEnumerable(Of TResult)

類型參數

TSource

source 項目的類型。The type of the elements of source.

TKey

所傳回的索引鍵類型keySelectorThe type of the key returned by keySelector.

TResult

所傳回之結果值的型別resultSelectorThe type of the result value returned by resultSelector.

參數

source
IEnumerable<TSource>

IEnumerable<T>群組其項目。An IEnumerable<T> whose elements to group.

keySelector
Func<TSource,TKey>

用來擷取各項目之索引鍵的函式。A function to extract the key for each element.

resultSelector
Func<TKey,IEnumerable<TSource>,TResult>

用來從各個群組建立結果值的函式。A function to create a result value from each group.

傳回

IEnumerable<TResult>

型別的項目集合TResult其中每個項目代表投影的群組和其索引鍵。A collection of elements of type TResult where each element represents a projection over a group and its key.

範例

下列程式碼範例示範如何使用GroupBy<TSource,TKey,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TKey,IEnumerable<TSource>,TResult>)分組序列的項目,以及專案的型別的結果序列TResultThe following code example demonstrates how to use GroupBy<TSource,TKey,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TKey,IEnumerable<TSource>,TResult>) to group the elements of a sequence and project a sequence of results of type TResult.

class Pet
{
    public string Name { get; set; }
    public double Age { get; set; }
}

public static void GroupByEx3()
{
    // Create a list of pets.
    List<Pet> petsList =
        new List<Pet>{ new Pet { Name="Barley", Age=8.3 },
                       new Pet { Name="Boots", Age=4.9 },
                       new Pet { Name="Whiskers", Age=1.5 },
                       new Pet { Name="Daisy", Age=4.3 } };

    // Group Pet objects by the Math.Floor of their age.
    // Then project an anonymous type from each group
    // that consists of the key, the count of the group's
    // elements, and the minimum and maximum age in the group.
    var query = petsList.GroupBy(
        pet => Math.Floor(pet.Age),
        (age, pets) => new
        {
            Key = age,
            Count = pets.Count(),
            Min = pets.Min(pet => pet.Age),
            Max = pets.Max(pet => pet.Age)
        });

    // Iterate over each anonymous type.
    foreach (var result in query)
    {
        Console.WriteLine("\nAge group: " + result.Key);
        Console.WriteLine("Number of pets in this age group: " + result.Count);
        Console.WriteLine("Minimum age: " + result.Min);
        Console.WriteLine("Maximum age: " + result.Max);
    }

    /*  This code produces the following output:
     
        Age group: 8
        Number of pets in this age group: 1
        Minimum age: 8.3
        Maximum age: 8.3
     
        Age group: 4
        Number of pets in this age group: 2
        Minimum age: 4.3
        Maximum age: 4.9
     
        Age group: 1
        Number of pets in this age group: 1
        Minimum age: 1.5
        Maximum age: 1.5
    */
}
Structure Pet
    Public Name As String
    Public Age As Double
End Structure

Public Sub GroupByEx3()
    ' Create a list of pets.
    Dim petsList As New List(Of Pet)(New Pet() _
                         {New Pet With {.Name = "Barley", .Age = 8.3},
                          New Pet With {.Name = "Boots", .Age = 4.9},
                          New Pet With {.Name = "Whiskers", .Age = 1.5},
                          New Pet With {.Name = "Daisy", .Age = 4.3}})

    ' Group Pet objects by the Math.Floor of their age.
    ' Then project an anonymous type from each group
    ' that consists of the key, the count of the group's
    ' elements, and the minimum and maximum age in the group.
    Dim query = petsList.GroupBy(
Function(pet) Math.Floor(pet.Age),
Function(age, pets) New With
    {.Key = age,
    .Count = pets.Count(),
    .Min = pets.Min(Function(pet) pet.Age),
    .Max = pets.Max(Function(Pet) Pet.Age)}
)

    Dim output As New System.Text.StringBuilder
    ' Iterate over each anonymous type.
    For Each result In query
        output.AppendLine(vbCrLf & "Age group: " & result.Key)
        output.AppendLine("Number of pets in this age group: " & result.Count)
        output.AppendLine("Minimum age: " & result.Min)
        output.AppendLine("Maximum age: " & result.Max)
    Next

    ' Display the output.
    MsgBox(output.ToString)
End Sub

' This code produces the following output:

' Age group: 8
' Number of pets in this age group: 1
' Minimum age: 8.3
' Maximum age: 8.3
'
' Age group: 4
' Number of pets in this age group: 2
' Minimum age: 4.3
' Maximum age: 4.9
'
' Age group: 1
' Number of pets in this age group: 1
' Minimum age: 1.5
' Maximum age: 1.5

備註

在查詢運算式語法中, group by (Visual C#) 或Group By Into(Visual Basic) 子句會轉譯成的引動過程GroupByIn query expression syntax, a group by (Visual C#) or Group By Into (Visual Basic) clause translates to an invocation of GroupBy.

另請參閱

GroupBy<TSource,TKey,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TKey,IEnumerable<TSource>,TResult>, IEqualityComparer<TKey>) GroupBy<TSource,TKey,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TKey,IEnumerable<TSource>,TResult>, IEqualityComparer<TKey>) GroupBy<TSource,TKey,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TKey,IEnumerable<TSource>,TResult>, IEqualityComparer<TKey>) GroupBy<TSource,TKey,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TKey,IEnumerable<TSource>,TResult>, IEqualityComparer<TKey>)

依據指定的索引鍵選取器函式來群組序列的項目,並從每個群組及其索引鍵建立結果值。Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. 索引鍵是使用指定的比較子來進行比較。The keys are compared by using a specified comparer.

public:
generic <typename TSource, typename TKey, typename TResult>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::IEnumerable<TResult> ^ GroupBy(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector, Func<TKey, System::Collections::Generic::IEnumerable<TSource> ^, TResult> ^ resultSelector, System::Collections::Generic::IEqualityComparer<TKey> ^ comparer);
public static System.Collections.Generic.IEnumerable<TResult> GroupBy<TSource,TKey,TResult> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, Func<TKey,System.Collections.Generic.IEnumerable<TSource>,TResult> resultSelector, System.Collections.Generic.IEqualityComparer<TKey> comparer);
static member GroupBy : seq<'Source> * Func<'Source, 'Key> * Func<'Key, seq<'Source>, 'Result> * System.Collections.Generic.IEqualityComparer<'Key> -> seq<'Result>
<Extension()>
Public Function GroupBy(Of TSource, TKey, TResult) (source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey), resultSelector As Func(Of TKey, IEnumerable(Of TSource), TResult), comparer As IEqualityComparer(Of TKey)) As IEnumerable(Of TResult)

類型參數

TSource

source 項目的類型。The type of the elements of source.

TKey

所傳回的索引鍵類型keySelectorThe type of the key returned by keySelector.

TResult

所傳回之結果值的型別resultSelectorThe type of the result value returned by resultSelector.

參數

source
IEnumerable<TSource>

IEnumerable<T>群組其項目。An IEnumerable<T> whose elements to group.

keySelector
Func<TSource,TKey>

用來擷取各項目之索引鍵的函式。A function to extract the key for each element.

resultSelector
Func<TKey,IEnumerable<TSource>,TResult>

用來從各個群組建立結果值的函式。A function to create a result value from each group.

comparer
IEqualityComparer<TKey>

IEqualityComparer<T>來比較索引鍵。An IEqualityComparer<T> to compare keys with.

傳回

IEnumerable<TResult>

型別的項目集合TResult其中每個項目代表投影的群組和其索引鍵。A collection of elements of type TResult where each element represents a projection over a group and its key.

另請參閱

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

分組依據指定的索引鍵選取器函式序列的項目。Groups the elements of a sequence according to a specified key selector function.

public:
generic <typename TSource, typename TKey>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::IEnumerable<System::Linq::IGrouping<TKey, TSource> ^> ^ GroupBy(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector);
public static System.Collections.Generic.IEnumerable<System.Linq.IGrouping<TKey,TSource>> GroupBy<TSource,TKey> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector);
static member GroupBy : seq<'Source> * Func<'Source, 'Key> -> seq<System.Linq.IGrouping<'Key, 'Source>>
<Extension()>
Public Function GroupBy(Of TSource, TKey) (source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey)) As IEnumerable(Of IGrouping(Of TKey, TSource))

類型參數

TSource

source 項目的類型。The type of the elements of source.

TKey

所傳回的索引鍵類型keySelectorThe type of the key returned by keySelector.

參數

source
IEnumerable<TSource>

IEnumerable<T>群組其項目。An IEnumerable<T> whose elements to group.

keySelector
Func<TSource,TKey>

用來擷取各項目之索引鍵的函式。A function to extract the key for each element.

傳回

IEnumerable<IGrouping<TKey,TSource>>

C# 中的 IEnumerable<IGrouping<TKey, TSource>> 或 Visual Basic 中的 IEnumerable(Of IGrouping(Of TKey, TSource)),其中每個 IGrouping<TKey,TElement> 物件包含一序列的物件序和一個索引鍵。An IEnumerable<IGrouping<TKey, TSource>> in C# or IEnumerable(Of IGrouping(Of TKey, TSource)) in Visual Basic where each IGrouping<TKey,TElement> object contains a sequence of objects and a key.

例外狀況

sourcekeySelectornullsource or keySelector is null.

備註

實作這個方法是使用延後的執行。This method is implemented by using deferred execution. 立即傳回值是儲存,才能執行此動作的所有資訊的物件。The immediate return value is an object that stores all the information that is required to perform the action. 這個方法所表示的查詢不會執行直到列舉物件可以藉由呼叫其GetEnumerator方法直接或透過foreachVisual C# 中或For EachVisual Basic 中。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.

GroupBy<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>)方法傳回的集合IGrouping<TKey,TElement>物件,一個用於每個發現的相異索引鍵。The GroupBy<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>) method returns a collection of IGrouping<TKey,TElement> objects, one for each distinct key that was encountered. IGrouping<TKey,TElement>IEnumerable<T>也具有其項目相關聯的索引鍵。An IGrouping<TKey,TElement> is an IEnumerable<T> that also has a key associated with its elements.

IGrouping<TKey,TElement>物件產生根據順序中的項目順序source產生第一個索引鍵,每個IGrouping<TKey,TElement>The IGrouping<TKey,TElement> objects are yielded in an order based on the order of the elements in source that produced the first key of each IGrouping<TKey,TElement>. 在群組中的項目中出現的順序產生sourceElements in a grouping are yielded in the order they appear in source.

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

在查詢運算式語法中, group by (Visual C#) 或Group By Into(Visual Basic) 子句會轉譯成的引動過程GroupByIn query expression syntax, a group by (Visual C#) or Group By Into (Visual Basic) clause translates to an invocation of GroupBy. 如需詳細資訊和使用方式範例,請參閱 < group 子句By 子句群組For more information and usage examples, see group clause and Group By Clause.

另請參閱

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

群組的順序,根據指定的索引鍵選取器函式和比較使用指定的比較子索引鍵的項目。Groups the elements of a sequence according to a specified key selector function and compares the keys by using a specified comparer.

public:
generic <typename TSource, typename TKey>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::IEnumerable<System::Linq::IGrouping<TKey, TSource> ^> ^ GroupBy(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, TKey> ^ keySelector, System::Collections::Generic::IEqualityComparer<TKey> ^ comparer);
public static System.Collections.Generic.IEnumerable<System.Linq.IGrouping<TKey,TSource>> GroupBy<TSource,TKey> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,TKey> keySelector, System.Collections.Generic.IEqualityComparer<TKey> comparer);
static member GroupBy : seq<'Source> * Func<'Source, 'Key> * System.Collections.Generic.IEqualityComparer<'Key> -> seq<System.Linq.IGrouping<'Key, 'Source>>
<Extension()>
Public Function GroupBy(Of TSource, TKey) (source As IEnumerable(Of TSource), keySelector As Func(Of TSource, TKey), comparer As IEqualityComparer(Of TKey)) As IEnumerable(Of IGrouping(Of TKey, TSource))

類型參數

TSource

source 項目的類型。The type of the elements of source.

TKey

所傳回的索引鍵類型keySelectorThe type of the key returned by keySelector.

參數

source
IEnumerable<TSource>

IEnumerable<T>群組其項目。An IEnumerable<T> whose elements to group.

keySelector
Func<TSource,TKey>

用來擷取各項目之索引鍵的函式。A function to extract the key for each element.

comparer
IEqualityComparer<TKey>

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

傳回

IEnumerable<IGrouping<TKey,TSource>>

C# 中的 IEnumerable<IGrouping<TKey, TSource>> 或 Visual Basic 中的 IEnumerable(Of IGrouping(Of TKey, TSource)),其中每個 IGrouping<TKey,TElement> 物件包含一個物件集合和一個索引鍵。An IEnumerable<IGrouping<TKey, TSource>> in C# or IEnumerable(Of IGrouping(Of TKey, TSource)) in Visual Basic where each IGrouping<TKey,TElement> object contains a collection of objects and a key.

例外狀況

sourcekeySelectornullsource or keySelector is null.

備註

實作這個方法是使用延後的執行。This method is implemented by using deferred execution. 立即傳回值是儲存,才能執行此動作的所有資訊的物件。The immediate return value is an object that stores all the information that is required to perform the action. 這個方法所表示的查詢不會執行直到列舉物件可以藉由呼叫其GetEnumerator方法直接或透過foreachVisual C# 中或For EachVisual Basic 中。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.

GroupBy<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IEqualityComparer<TKey>)方法傳回的集合IGrouping<TKey,TElement>物件,一個用於每個發現的相異索引鍵。The GroupBy<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IEqualityComparer<TKey>) method returns a collection of IGrouping<TKey,TElement> objects, one for each distinct key that was encountered. IGrouping<TKey,TElement>IEnumerable<T>也具有其項目相關聯的索引鍵。An IGrouping<TKey,TElement> is an IEnumerable<T> that also has a key associated with its elements.

IGrouping<TKey,TElement>物件產生根據順序中的項目順序source產生第一個索引鍵,每個IGrouping<TKey,TElement>The IGrouping<TKey,TElement> objects are yielded in an order based on the order of the elements in source that produced the first key of each IGrouping<TKey,TElement>. 在群組中的項目中出現的順序產生sourceElements in a grouping are yielded in the order they appear in source.

如果comparernull,預設相等比較子Default用來比較索引鍵。If comparer is null, the default equality comparer Default is used to compare keys.

如果兩個金鑰會被視為相等於根據comparer,第一個索引鍵會被選為該群組的索引鍵。If two keys are considered equal according to comparer, the first key is chosen as the key for that grouping.

在查詢運算式語法中, group by (Visual C#) 或Group By Into(Visual Basic) 子句會轉譯成的引動過程GroupByIn query expression syntax, a group by (Visual C#) or Group By Into (Visual Basic) clause translates to an invocation of GroupBy. 如需詳細資訊和使用方式範例,請參閱 < group 子句By 子句群組For more information and usage examples, see group clause and Group By Clause.

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