Enumerable.Except Enumerable.Except Enumerable.Except Enumerable.Except Method

Produce la differenza insiemistica di due sequenze utilizzando l'operatore di confronto uguaglianze predefinito per confrontare valori.Produces the set difference of two sequences by using the default equality comparer to compare values.

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::IEnumerable<TSource> ^ Except(System::Collections::Generic::IEnumerable<TSource> ^ first, System::Collections::Generic::IEnumerable<TSource> ^ second);

public static System.Collections.Generic.IEnumerable<TSource> Except<TSource> (this System.Collections.Generic.IEnumerable<TSource> first, System.Collections.Generic.IEnumerable<TSource> second);

static member Except : seq<'Source> * seq<'Source> -> seq<'Source>

<Extension()>
Public Function Except(Of TSource) (first As IEnumerable(Of TSource), second As IEnumerable(Of TSource)) As IEnumerable(Of TSource)

Parametri di tipo

Parametri

Restituisce

Eccezioni

Esempi

Esempio di codice seguente viene illustrato come utilizzare il Except<TSource>(IEnumerable<TSource>, IEnumerable<TSource>) per confrontare due sequenze di numeri e restituire gli elementi che vengono visualizzati solo nella prima sequenza.The following code example demonstrates how to use the Except<TSource>(IEnumerable<TSource>, IEnumerable<TSource>) method to compare two sequences of numbers and return elements that appear only in the first sequence.

double[] numbers1 = { 2.0, 2.0, 2.1, 2.2, 2.3, 2.3, 2.4, 2.5 };
double[] numbers2 = { 2.2 };

IEnumerable<double> onlyInFirstSet = numbers1.Except(numbers2);

foreach (double number in onlyInFirstSet)
    Console.WriteLine(number);

/*
 This code produces the following output:

 2
 2.1
 2.3
 2.4
 2.5
*/

' Create two arrays of doubles.
Dim numbers1() As Double = { 2.0, 2.0, 2.1, 2.2, 2.3, 2.3, 2.4, 2.5 }
Dim numbers2() As Double = {2.2}

' Select the elements from the first array that are not
' in the second array.
Dim onlyInFirstSet As IEnumerable(Of Double) = numbers1.Except(numbers2)

Dim output As New System.Text.StringBuilder
For Each number As Double In onlyInFirstSet
    output.AppendLine(number)
Next

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

' This code produces the following output:
'
' 2
' 2.1
' 2.3
' 2.4
' 2.5

Se si desidera confrontare le sequenze di oggetti di un tipo di dati personalizzate, è necessario implementare il IEquatable<T> generica interfaccia in una classe helper.If you want to compare sequences of objects of some custom data type, you have to implement the IEquatable<T> generic interface in a helper class. Esempio di codice seguente viene illustrato come implementare questa interfaccia in un tipo di dati personalizzato ed eseguire l'override GetHashCode e Equals metodi.The following code example shows how to implement this interface in a custom data type and override GetHashCode and Equals methods.

public class ProductA: IEquatable<ProductA>
{
    public string Name { get; set; }
    public int Code { get; set; }

    public bool Equals(ProductA other)
    {
        if (other is null)
            return false;

        return this.Name == other.Name && this.Code == other.Code;
    }

    public override bool Equals(object obj) => Equals(obj as ProductA);
    public override int GetHashCode() => (Name, Code).GetHashCode();
}

Public Class ProductA
    Inherits IEquatable(Of ProductA)

    Public Property Name As String
    Public Property Code As Integer

    Public Function Equals(ByVal other As ProductA) As Boolean
        If other Is Nothing Then Return False
        Return Me.Name = other.Name AndAlso Me.Code = other.Code
    End Function

    Public Overrides Function Equals(ByVal obj As Object) As Boolean
        Return Equals(TryCast(obj, ProductA))
    End Function

    Public Overrides Function GetHashCode() As Integer
        Return (Name, Code).GetHashCode()
    End Function

End Class

Dopo aver implementato questa interfaccia, è possibile usare le sequenze di ProductA oggetti nel Except<TSource>(IEnumerable<TSource>, IEnumerable<TSource>) metodo, come illustrato nell'esempio seguente:After you implement this interface, you can use sequences of ProductA objects in the Except<TSource>(IEnumerable<TSource>, IEnumerable<TSource>) method, as shown in the following example:

ProductA[] fruits1 = { new ProductA { Name = "apple", Code = 9 }, 
                       new ProductA { Name = "orange", Code = 4 },
                        new ProductA { Name = "lemon", Code = 12 } };

ProductA[] fruits2 = { new ProductA { Name = "apple", Code = 9 } };

//Get all the elements from the first array
//except for the elements from the second array.

IEnumerable<ProductA> except =
    fruits1.Except(fruits2);

foreach (var product in except)
    Console.WriteLine(product.Name + " " + product.Code);

/*
  This code produces the following output:
 
  orange 4
  lemon 12
*/

Dim fruits1() As Product = 
    {New Product With {.Name = "apple", .Code = 9}, 
     New Product With {.Name = "orange", .Code = 4}, 
     New Product With {.Name = "lemon", .Code = 12}}

Dim fruits2() As Product = 
    {New Product With {.Name = "apple", .Code = 9}}

' Get all the elements from the first array
' except for the elements from the second array.

Dim except = fruits1.Except(fruits2)

For Each product In except
    Console.WriteLine(product.Name & " " & product.Code)
Next

' This code produces the following output:
'
' apple 9
' orange 4
' lemon 12

Commenti

Questo metodo viene implementato tramite l'esecuzione posticipata.This method is implemented by using deferred execution. Il controllo immediato valore restituito 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 fino a quando l'oggetto viene enumerata chiamando relativi GetEnumerator metodo direttamente o tramite 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.

Operatore di uguaglianza predefinito, Default, viene usata per confrontare i valori dei tipi.The default equality comparer, Default, is used to compare values of the types. Per confrontare un tipo di dati personalizzato, è necessario eseguire l'override di Equals e il GetHashCode metodi e, facoltativamente, implementare il IEquatable<T> interfaccia generica di tipo personalizzato.To compare a custom data type, you need to override the Equals and the GetHashCode methods, and optionally implement the IEquatable<T> generic interface in the custom type. Per altre informazioni, vedere la proprietà Default.For more information, see the Default property.

Produce la differenza insiemistica di due sequenze utilizzando l'oggetto specificato IEqualityComparer<T> per confrontare i valori.Produces the set difference of two sequences by using the specified IEqualityComparer<T> to compare values.

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::IEnumerable<TSource> ^ Except(System::Collections::Generic::IEnumerable<TSource> ^ first, System::Collections::Generic::IEnumerable<TSource> ^ second, System::Collections::Generic::IEqualityComparer<TSource> ^ comparer);

public static System.Collections.Generic.IEnumerable<TSource> Except<TSource> (this System.Collections.Generic.IEnumerable<TSource> first, System.Collections.Generic.IEnumerable<TSource> second, System.Collections.Generic.IEqualityComparer<TSource> comparer);

static member Except : seq<'Source> * seq<'Source> * System.Collections.Generic.IEqualityComparer<'Source> -> seq<'Source>

<Extension()>
Public Function Except(Of TSource) (first As IEnumerable(Of TSource), second As IEnumerable(Of TSource), comparer As IEqualityComparer(Of TSource)) As IEnumerable(Of TSource)

Parametri di tipo

Parametri

Restituisce

Eccezioni

Esempi

Se si desidera confrontare le sequenze di oggetti di un tipo di dati personalizzate, è necessario implementare il IEqualityComparer<T> generica interfaccia in una classe helper.If you want to compare sequences of objects of some custom data type, you have to implement the IEqualityComparer<T> generic interface in a helper class. Esempio di codice seguente viene illustrato come implementare questa interfaccia in un tipo di dati personalizzati e fornire GetHashCode e Equals metodi.The following code example shows how to implement this interface in a custom data type and provide GetHashCode and Equals methods. Nell'esempio seguente viene illustrato come implementare un operatore di confronto di uguaglianze che può essere usato nel Except (metodo).The following example shows how to implement an equality comparer that can be used in the Except method.

public class Product
{
    public string Name { get; set; }
    public int Code { get; set; }
}

// Custom comparer for the Product class
class ProductComparer : IEqualityComparer<Product>
{
    // Products are equal if their names and product numbers are equal.
    public bool Equals(Product x, Product y)
    {
       
        //Check whether the compared objects reference the same data.
        if (Object.ReferenceEquals(x, y)) return true;

        //Check whether any of the compared objects is null.
        if (Object.ReferenceEquals(x, null) || Object.ReferenceEquals(y, null))
            return false;

        //Check whether the products' properties are equal.
        return x.Code == y.Code && x.Name == y.Name;
    }

    // If Equals() returns true for a pair of objects 
    // then GetHashCode() must return the same value for these objects.

    public int GetHashCode(Product product)
    {
        //Check whether the object is null
        if (Object.ReferenceEquals(product, null)) return 0;

        //Get hash code for the Name field if it is not null.
        int hashProductName = product.Name == null ? 0 : product.Name.GetHashCode();

        //Get hash code for the Code field.
        int hashProductCode = product.Code.GetHashCode();

        //Calculate the hash code for the product.
        return hashProductName ^ hashProductCode;
    }

}

Public Class Product
    Public Property Name As String
    Public Property Code As Integer
End Class

' Custom comparer for the Product class
Public Class ProductComparer
    Implements IEqualityComparer(Of Product)

    Public Function Equals1(
        ByVal x As Product, 
        ByVal y As Product
        ) As Boolean Implements IEqualityComparer(Of Product).Equals

        ' Check whether the compared objects reference the same data.
        If x Is y Then Return True

        'Check whether any of the compared objects is null.
        If x Is Nothing OrElse y Is Nothing Then Return False

        ' Check whether the products' properties are equal.
        Return (x.Code = y.Code) AndAlso (x.Name = y.Name)
    End Function

    Public Function GetHashCode1(
        ByVal product As Product
        ) As Integer Implements IEqualityComparer(Of Product).GetHashCode

        ' Check whether the object is null.
        If product Is Nothing Then Return 0

        ' Get hash code for the Name field if it is not null.
        Dim hashProductName = 
            If(product.Name Is Nothing, 0, product.Name.GetHashCode())

        ' Get hash code for the Code field.
        Dim hashProductCode = product.Code.GetHashCode()

        ' Calculate the hash code for the product.
        Return hashProductName Xor hashProductCode
    End Function
End Class

Dopo aver implementato questo operatore di confronto, è possibile usare le sequenze di Product oggetti nel Except metodo, come illustrato nell'esempio seguente:After you implement this comparer, you can use sequences of Product objects in the Except method, as shown in the following example:

Product[] fruits1 = { new Product { Name = "apple", Code = 9 }, 
                       new Product { Name = "orange", Code = 4 },
                        new Product { Name = "lemon", Code = 12 } };

Product[] fruits2 = { new Product { Name = "apple", Code = 9 } };

//Get all the elements from the first array
//except for the elements from the second array.

IEnumerable<Product> except =
    fruits1.Except(fruits2, new ProductComparer());

foreach (var product in except)
    Console.WriteLine(product.Name + " " + product.Code);

/*
  This code produces the following output:
 
  orange 4
  lemon 12
*/

Dim fruits1() As Product = 
    {New Product With {.Name = "apple", .Code = 9}, 
     New Product With {.Name = "orange", .Code = 4}, 
     New Product With {.Name = "lemon", .Code = 12}}

Dim fruits2() As Product = 
    {New Product With {.Name = "apple", .Code = 9}}

' Get all the elements from the first array
' except for the elements from the second array.

Dim except = fruits1.Except(fruits2, New ProductComparer())

For Each product In except
    Console.WriteLine(product.Name & " " & product.Code)
Next

' This code produces the following output:
'
' orange 4
' lemon 12

Commenti

Se comparer viene null, l'operatore di confronto uguaglianze predefinito, Default, viene usata per confrontare valori.If comparer is null, the default equality comparer, Default, is used to compare values.