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

Definizione

Raggruppa gli elementi di una sequenza.Groups the elements of a sequence.

Overload

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>)

Raggruppa gli elementi di una sequenza in base a una funzione del selettore principale specificata e crea un valore risultante da ciascun gruppo e relativa chiave.Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. Gli elementi di ogni gruppo vengono proiettati usando una funzione specificata.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>)

Raggruppa gli elementi di una sequenza in base a una funzione del selettore principale specificata e crea un valore risultante da ciascun gruppo e relativa chiave.Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. I valori delle chiavi vengono confrontati usando un operatore di confronto specificato e gli elementi di ogni gruppo vengono proiettati usando una funzione specificata.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>)

Raggruppa gli elementi di una sequenza in base a una funzione specificata del selettore principale e proietta gli elementi di ogni gruppo utilizzando una funzione specificata.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>)

Raggruppa gli elementi di una sequenza secondo una specificata funzione del selettore principale.Groups the elements of a sequence according to a key selector function. Le chiavi vengono confrontate usando un operatore di confronto e gli elementi di ogni gruppo vengono proiettati usando una funzione specificata.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>)

Raggruppa gli elementi di una sequenza in base a una funzione del selettore principale specificata e crea un valore risultante da ciascun gruppo e relativa chiave.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>)

Raggruppa gli elementi di una sequenza in base a una funzione del selettore principale specificata e crea un valore risultante da ciascun gruppo e relativa chiave.Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. Le chiavi vengono confrontati usando un operatore di confronto specificato.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>)

Raggruppa gli elementi di una sequenza secondo una specificata funzione del selettore principale.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>)

Raggruppa gli elementi di una sequenza secondo una specificata funzione del selettore principale e confronta le chiavi utilizzando un operatore di confronto specificato.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>)

Raggruppa gli elementi di una sequenza in base a una funzione del selettore principale specificata e crea un valore risultante da ciascun gruppo e relativa chiave.Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. Gli elementi di ogni gruppo vengono proiettati usando una funzione specificata.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)

Parametri di tipo

TSource

Tipo degli elementi di source.The type of the elements of source.

TKey

Tipo della chiave restituita dall'oggetto keySelector.The type of the key returned by keySelector.

TElement

Tipo degli elementi contenuti in ciascun oggetto IGrouping<TKey,TElement>.The type of the elements in each IGrouping<TKey,TElement>.

TResult

Tipo del valore restituito dall'oggetto resultSelector.The type of the result value returned by resultSelector.

Parametri

source
IEnumerable<TSource>

Oggetto IEnumerable<T> i cui elementi sono da raggruppare.An IEnumerable<T> whose elements to group.

keySelector
Func<TSource,TKey>

Funzione per estrarre la chiave per ogni elemento.A function to extract the key for each element.

elementSelector
Func<TSource,TElement>

Funzione per eseguire il mapping di ogni elemento di origine a un elemento in un oggetto IGrouping<TKey,TElement>.A function to map each source element to an element in an IGrouping<TKey,TElement>.

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

Funzione per creare un valore di risultato da ogni gruppo.A function to create a result value from each group.

Restituisce

IEnumerable<TResult>

Raccolta di elementi di tipo TResult dove ogni elemento rappresenta una proiezione su un gruppo e sulla relativa chiave.A collection of elements of type TResult where each element represents a projection over a group and its key.

Esempi

Nell'esempio di codice riportato di seguito viene GroupBy<TSource,TKey,TElement,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, Func<TKey,IEnumerable<TElement>,TResult>) illustrato come utilizzare per raggruppare gli elementi proiettati di una sequenza e quindi proiettare una TResultsequenza di risultati di tipo.The 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

Commenti

Nella sintassi delle espressioni di query group by una clausola C#(Visual Group By Into ) o (Visual Basic) viene convertita in una chiamata di GroupBy.In query expression syntax, a group by (Visual C#) or Group By Into (Visual Basic) clause translates to an invocation of GroupBy.

Vedi anche

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>)

Raggruppa gli elementi di una sequenza in base a una funzione del selettore principale specificata e crea un valore risultante da ciascun gruppo e relativa chiave.Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. I valori delle chiavi vengono confrontati usando un operatore di confronto specificato e gli elementi di ogni gruppo vengono proiettati usando una funzione specificata.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)

Parametri di tipo

TSource

Tipo degli elementi di source.The type of the elements of source.

TKey

Tipo della chiave restituita dall'oggetto keySelector.The type of the key returned by keySelector.

TElement

Tipo degli elementi contenuti in ciascun oggetto IGrouping<TKey,TElement>.The type of the elements in each IGrouping<TKey,TElement>.

TResult

Tipo del valore restituito dall'oggetto resultSelector.The type of the result value returned by resultSelector.

Parametri

source
IEnumerable<TSource>

Oggetto IEnumerable<T> i cui elementi sono da raggruppare.An IEnumerable<T> whose elements to group.

keySelector
Func<TSource,TKey>

Funzione per estrarre la chiave per ogni elemento.A function to extract the key for each element.

elementSelector
Func<TSource,TElement>

Funzione per eseguire il mapping di ogni elemento di origine a un elemento in un oggetto IGrouping<TKey,TElement>.A function to map each source element to an element in an IGrouping<TKey,TElement>.

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

Funzione per creare un valore di risultato da ogni gruppo.A function to create a result value from each group.

comparer
IEqualityComparer<TKey>

Oggetto IEqualityComparer<T> con cui confrontare le chiavi.An IEqualityComparer<T> to compare keys with.

Restituisce

IEnumerable<TResult>

Raccolta di elementi di tipo TResult dove ogni elemento rappresenta una proiezione su un gruppo e sulla relativa chiave.A collection of elements of type TResult where each element represents a projection over a group and its key.

Vedi anche

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>)

Raggruppa gli elementi di una sequenza in base a una funzione specificata del selettore principale e proietta gli elementi di ogni gruppo utilizzando una funzione specificata.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))

Parametri di tipo

TSource

Tipo degli elementi di source.The type of the elements of source.

TKey

Tipo della chiave restituita dall'oggetto keySelector.The type of the key returned by keySelector.

TElement

Tipo degli elementi contenuti nell'oggetto IGrouping<TKey,TElement>.The type of the elements in the IGrouping<TKey,TElement>.

Parametri

source
IEnumerable<TSource>

Oggetto IEnumerable<T> i cui elementi sono da raggruppare.An IEnumerable<T> whose elements to group.

keySelector
Func<TSource,TKey>

Funzione per estrarre la chiave per ogni elemento.A function to extract the key for each element.

elementSelector
Func<TSource,TElement>

Funzione per eseguire il mapping di ogni elemento di origine a un elemento nell’oggetto IGrouping<TKey,TElement>.A function to map each source element to an element in the IGrouping<TKey,TElement>.

Restituisce

IEnumerable<IGrouping<TKey,TElement>>

Un elemento IEnumerable<IGrouping<TKey, TElement>> in C# o IEnumerable(Of IGrouping(Of TKey, TElement)) in Visual Basic in cui ogni oggetto IGrouping<TKey,TElement> contiene una raccolta di oggetti di tipo TElement e una chiave.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.

Eccezioni

Il parametro source, il parametro keySelector o il parametro elementSelector è null.source or keySelector or elementSelector is null.

Esempi

Nell'esempio di codice riportato di seguito viene GroupBy<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>) illustrato come utilizzare per raggruppare gli elementi di una sequenza.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

Nella sintassi delle espressioni di query group by una clausola C#(Visual Group By Into ) o (Visual Basic) viene convertita in una chiamata di GroupBy.In query expression syntax, a group by (Visual C#) or Group By Into (Visual Basic) clause translates to an invocation of GroupBy. La conversione dell'espressione di query nell'esempio seguente è equivalente alla query nell'esempio precedente.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

Nota

In un'espressione C# di query Visual o Visual Basic le espressioni di selezione di elementi e chiavi si verificano nell'ordine inverso rispetto alle posizioni degli argomenti GroupBy<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>) in una chiamata al metodo.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.

Commenti

Questo metodo viene implementato tramite l'esecuzione posticipata.This method is implemented by using deferred execution. Il valore restituito immediato è un oggetto che archivia tutte le informazioni necessarie per eseguire l'azione.The immediate return value is an object that stores all the information that is required to perform the action. La query rappresentata da questo metodo non viene eseguita finché l'oggetto non viene enumerato chiamando il GetEnumerator relativo metodo direttamente o utilizzando foreach in Visual C# o For Each in Visual Basic.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.

Il GroupBy<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>) metodo restituisce una raccolta di IGrouping<TKey,TElement> oggetti, uno per ogni chiave DISTINCT che è stata rilevata.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. Un IGrouping<TKey,TElement> oggetto è IEnumerable<T> un oggetto che dispone anche di una chiave associata ai relativi elementi.An IGrouping<TKey,TElement> is an IEnumerable<T> that also has a key associated with its elements.

Gli IGrouping<TKey,TElement> oggetti vengono restituiti in un ordine in base all'ordine degli elementi in source che hanno prodotto la prima chiave di ogni 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>. Gli elementi in un raggruppamento vengono restituiti nell'ordine in cui vengono visualizzati sourcegli elementi che li hanno generati.Elements in a grouping are yielded in the order that the elements that produced them appear in source.

Per confrontare le chiavi Default viene usato l'operatore di confronto di uguaglianza predefinito.The default equality comparer Default is used to compare keys.

Vedi anche

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>)

Raggruppa gli elementi di una sequenza secondo una specificata funzione del selettore principale.Groups the elements of a sequence according to a key selector function. Le chiavi vengono confrontate usando un operatore di confronto e gli elementi di ogni gruppo vengono proiettati usando una funzione specificata.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))

Parametri di tipo

TSource

Tipo degli elementi di source.The type of the elements of source.

TKey

Tipo della chiave restituita dall'oggetto keySelector.The type of the key returned by keySelector.

TElement

Tipo degli elementi contenuti nell'oggetto IGrouping<TKey,TElement>.The type of the elements in the IGrouping<TKey,TElement>.

Parametri

source
IEnumerable<TSource>

Oggetto IEnumerable<T> i cui elementi sono da raggruppare.An IEnumerable<T> whose elements to group.

keySelector
Func<TSource,TKey>

Funzione per estrarre la chiave per ogni elemento.A function to extract the key for each element.

elementSelector
Func<TSource,TElement>

Funzione per eseguire il mapping di ogni elemento di origine a un elemento in un oggetto IGrouping<TKey,TElement>.A function to map each source element to an element in an IGrouping<TKey,TElement>.

comparer
IEqualityComparer<TKey>

Oggetto IEqualityComparer<T> per confrontare le chiavi.An IEqualityComparer<T> to compare keys.

Restituisce

IEnumerable<IGrouping<TKey,TElement>>

Un elemento IEnumerable<IGrouping<TKey, TElement>> in C# o IEnumerable(Of IGrouping(Of TKey, TElement)) in Visual Basic in cui ogni oggetto IGrouping<TKey,TElement> contiene una raccolta di oggetti di tipo TElement e una chiave.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.

Eccezioni

Il parametro source, il parametro keySelector o il parametro elementSelector è null.source or keySelector or elementSelector is null.

Commenti

Questo metodo viene implementato tramite l'esecuzione posticipata.This method is implemented by using deferred execution. Il valore restituito immediato è un oggetto che archivia tutte le informazioni necessarie per eseguire l'azione.The immediate return value is an object that stores all the information that is required to perform the action. La query rappresentata da questo metodo non viene eseguita finché l'oggetto non viene enumerato chiamando il GetEnumerator relativo metodo direttamente o utilizzando foreach in Visual C# o For Each in Visual Basic.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.

Il GroupBy<TSource,TKey,TElement>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TSource,TElement>, IEqualityComparer<TKey>) metodo restituisce una raccolta di IGrouping<TKey,TElement> oggetti, uno per ogni chiave DISTINCT che è stata rilevata.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. Un IGrouping<TKey,TElement> oggetto è IEnumerable<T> un oggetto che dispone anche di una chiave associata ai relativi elementi.An IGrouping<TKey,TElement> is an IEnumerable<T> that also has a key associated with its elements.

Gli IGrouping<TKey,TElement> oggetti vengono restituiti in un ordine in base all'ordine degli elementi in source che hanno prodotto la prima chiave di ogni 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>. Gli elementi in un raggruppamento vengono restituiti nell'ordine in cui vengono visualizzati sourcegli elementi che li hanno generati.Elements in a grouping are yielded in the order that the elements that produced them appear in source.

Se comparer Default è null, viene utilizzato l'operatore di confronto di uguaglianza predefinito per confrontare le chiavi.If comparer is null, the default equality comparer Default is used to compare keys.

Se due chiavi sono considerate uguali in base comparera, viene scelta la prima chiave come chiave per il raggruppamento.If two keys are considered equal according to comparer, the first key is chosen as the key for that grouping.

Nella sintassi delle espressioni di query group by una clausola C#(Visual Group By Into ) o (Visual Basic) viene convertita in una chiamata di GroupBy.In query expression syntax, a group by (Visual C#) or Group By Into (Visual Basic) clause translates to an invocation of GroupBy. Per ulteriori informazioni ed esempi di utilizzo, vedere clausola Group e clausola Group by.For more information and usage examples, see group clause and Group By Clause.

Vedi anche

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>)

Raggruppa gli elementi di una sequenza in base a una funzione del selettore principale specificata e crea un valore risultante da ciascun gruppo e relativa chiave.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)

Parametri di tipo

TSource

Tipo degli elementi di source.The type of the elements of source.

TKey

Tipo della chiave restituita dall'oggetto keySelector.The type of the key returned by keySelector.

TResult

Tipo del valore restituito dall'oggetto resultSelector.The type of the result value returned by resultSelector.

Parametri

source
IEnumerable<TSource>

Oggetto IEnumerable<T> i cui elementi sono da raggruppare.An IEnumerable<T> whose elements to group.

keySelector
Func<TSource,TKey>

Funzione per estrarre la chiave per ogni elemento.A function to extract the key for each element.

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

Funzione per creare un valore di risultato da ogni gruppo.A function to create a result value from each group.

Restituisce

IEnumerable<TResult>

Raccolta di elementi di tipo TResult dove ogni elemento rappresenta una proiezione su un gruppo e sulla relativa chiave.A collection of elements of type TResult where each element represents a projection over a group and its key.

Esempi

Nell'esempio di codice riportato di seguito viene GroupBy<TSource,TKey,TResult>(IEnumerable<TSource>, Func<TSource,TKey>, Func<TKey,IEnumerable<TSource>,TResult>) illustrato come utilizzare per raggruppare gli elementi di una sequenza e proiettare una TResultsequenza di risultati di tipo.The 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

Commenti

Nella sintassi delle espressioni di query group by una clausola C#(Visual Group By Into ) o (Visual Basic) viene convertita in una chiamata di GroupBy.In query expression syntax, a group by (Visual C#) or Group By Into (Visual Basic) clause translates to an invocation of GroupBy.

Vedi anche

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>)

Raggruppa gli elementi di una sequenza in base a una funzione del selettore principale specificata e crea un valore risultante da ciascun gruppo e relativa chiave.Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. Le chiavi vengono confrontati usando un operatore di confronto specificato.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)

Parametri di tipo

TSource

Tipo degli elementi di source.The type of the elements of source.

TKey

Tipo della chiave restituita dall'oggetto keySelector.The type of the key returned by keySelector.

TResult

Tipo del valore restituito dall'oggetto resultSelector.The type of the result value returned by resultSelector.

Parametri

source
IEnumerable<TSource>

Oggetto IEnumerable<T> i cui elementi sono da raggruppare.An IEnumerable<T> whose elements to group.

keySelector
Func<TSource,TKey>

Funzione per estrarre la chiave per ogni elemento.A function to extract the key for each element.

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

Funzione per creare un valore di risultato da ogni gruppo.A function to create a result value from each group.

comparer
IEqualityComparer<TKey>

Oggetto IEqualityComparer<T> con cui confrontare le chiavi.An IEqualityComparer<T> to compare keys with.

Restituisce

IEnumerable<TResult>

Raccolta di elementi di tipo TResult dove ogni elemento rappresenta una proiezione su un gruppo e sulla relativa chiave.A collection of elements of type TResult where each element represents a projection over a group and its key.

Vedi anche

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>)

Raggruppa gli elementi di una sequenza secondo una specificata funzione del selettore principale.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))

Parametri di tipo

TSource

Tipo degli elementi di source.The type of the elements of source.

TKey

Tipo della chiave restituita dall'oggetto keySelector.The type of the key returned by keySelector.

Parametri

source
IEnumerable<TSource>

Oggetto IEnumerable<T> i cui elementi sono da raggruppare.An IEnumerable<T> whose elements to group.

keySelector
Func<TSource,TKey>

Funzione per estrarre la chiave per ogni elemento.A function to extract the key for each element.

Restituisce

IEnumerable<IGrouping<TKey,TSource>>

Elemento IEnumerable<IGrouping<TKey, TSource>> in C# o IEnumerable(Of IGrouping(Of TKey, TSource)) in Visual Basic in cui ogni oggetto IGrouping<TKey,TElement> contiene una sequenza di oggetti e una chiave.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.

Eccezioni

source o keySelector è null.source or keySelector is null.

Commenti

Questo metodo viene implementato tramite l'esecuzione posticipata.This method is implemented by using deferred execution. Il valore restituito immediato è un oggetto che archivia tutte le informazioni necessarie per eseguire l'azione.The immediate return value is an object that stores all the information that is required to perform the action. La query rappresentata da questo metodo non viene eseguita finché l'oggetto non viene enumerato chiamando il GetEnumerator relativo metodo direttamente o utilizzando foreach in Visual C# o For Each in Visual Basic.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.

Il GroupBy<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>) metodo restituisce una raccolta di IGrouping<TKey,TElement> oggetti, uno per ogni chiave DISTINCT che è stata rilevata.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. Un IGrouping<TKey,TElement> oggetto è IEnumerable<T> un oggetto che dispone anche di una chiave associata ai relativi elementi.An IGrouping<TKey,TElement> is an IEnumerable<T> that also has a key associated with its elements.

Gli IGrouping<TKey,TElement> oggetti vengono restituiti in un ordine in base all'ordine degli elementi in source che hanno prodotto la prima chiave di ogni 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>. Gli elementi in un raggruppamento vengono visualizzati nell'ordine in cui compaiono source.Elements in a grouping are yielded in the order they appear in source.

Per confrontare le chiavi Default viene usato l'operatore di confronto di uguaglianza predefinito.The default equality comparer Default is used to compare keys.

Nella sintassi delle espressioni di query group by una clausola C#(Visual Group By Into ) o (Visual Basic) viene convertita in una chiamata di GroupBy.In query expression syntax, a group by (Visual C#) or Group By Into (Visual Basic) clause translates to an invocation of GroupBy. Per ulteriori informazioni ed esempi di utilizzo, vedere clausola Group e clausola Group by.For more information and usage examples, see group clause and Group By Clause.

Vedi anche

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>)

Raggruppa gli elementi di una sequenza secondo una specificata funzione del selettore principale e confronta le chiavi utilizzando un operatore di confronto specificato.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))

Parametri di tipo

TSource

Tipo degli elementi di source.The type of the elements of source.

TKey

Tipo della chiave restituita dall'oggetto keySelector.The type of the key returned by keySelector.

Parametri

source
IEnumerable<TSource>

Oggetto IEnumerable<T> i cui elementi sono da raggruppare.An IEnumerable<T> whose elements to group.

keySelector
Func<TSource,TKey>

Funzione per estrarre la chiave per ogni elemento.A function to extract the key for each element.

comparer
IEqualityComparer<TKey>

Oggetto IEqualityComparer<T> per confrontare le chiavi.An IEqualityComparer<T> to compare keys.

Restituisce

IEnumerable<IGrouping<TKey,TSource>>

Un elemento IEnumerable<IGrouping<TKey, TSource>> in C# o IEnumerable(Of IGrouping(Of TKey, TSource)) in Visual Basic in cui ogni oggetto IGrouping<TKey,TElement> contiene una raccolta di oggetti e una chiave.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.

Eccezioni

source o keySelector è null.source or keySelector is null.

Commenti

Questo metodo viene implementato tramite l'esecuzione posticipata.This method is implemented by using deferred execution. Il valore restituito immediato è un oggetto che archivia tutte le informazioni necessarie per eseguire l'azione.The immediate return value is an object that stores all the information that is required to perform the action. La query rappresentata da questo metodo non viene eseguita finché l'oggetto non viene enumerato chiamando il GetEnumerator relativo metodo direttamente o utilizzando foreach in Visual C# o For Each in Visual Basic.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.

Il GroupBy<TSource,TKey>(IEnumerable<TSource>, Func<TSource,TKey>, IEqualityComparer<TKey>) metodo restituisce una raccolta di IGrouping<TKey,TElement> oggetti, uno per ogni chiave DISTINCT che è stata rilevata.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. Un IGrouping<TKey,TElement> oggetto è IEnumerable<T> un oggetto che dispone anche di una chiave associata ai relativi elementi.An IGrouping<TKey,TElement> is an IEnumerable<T> that also has a key associated with its elements.

Gli IGrouping<TKey,TElement> oggetti vengono restituiti in un ordine in base all'ordine degli elementi in source che hanno prodotto la prima chiave di ogni 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>. Gli elementi in un raggruppamento vengono visualizzati nell'ordine in cui compaiono source.Elements in a grouping are yielded in the order they appear in source.

Se comparer Default è null, viene utilizzato l'operatore di confronto di uguaglianza predefinito per confrontare le chiavi.If comparer is null, the default equality comparer Default is used to compare keys.

Se due chiavi sono considerate uguali in base comparera, viene scelta la prima chiave come chiave per il raggruppamento.If two keys are considered equal according to comparer, the first key is chosen as the key for that grouping.

Nella sintassi delle espressioni di query group by una clausola C#(Visual Group By Into ) o (Visual Basic) viene convertita in una chiamata di GroupBy.In query expression syntax, a group by (Visual C#) or Group By Into (Visual Basic) clause translates to an invocation of GroupBy. Per ulteriori informazioni ed esempi di utilizzo, vedere clausola Group e clausola Group by.For more information and usage examples, see group clause and Group By Clause.

Vedi anche

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