Enumerable.Except 方法

定義

產生兩個序列的差異。Produces the set difference of two sequences.

多載

Except<TSource>(IEnumerable<TSource>, IEnumerable<TSource>)

使用預設相等比較子來比較值,以便產生兩個序列的差異。Produces the set difference of two sequences by using the default equality comparer to compare values.

Except<TSource>(IEnumerable<TSource>, IEnumerable<TSource>, IEqualityComparer<TSource>)

使用指定的 IEqualityComparer<T> 來比較值,以便產生兩個序列的差異。Produces the set difference of two sequences by using the specified IEqualityComparer<T> to compare values.

備註

兩個集合的 [設定差異] 定義為第一個集合的成員,而不會出現在第二個集合中。The set difference of two sets is defined as the members of the first set that don't appear in the second set.

這個方法會傳回 first 中未出現在 second中的元素。This method returns those elements in first that don't appear in second. 它不會傳回 second 中未出現在 first中的元素。It doesn't return those elements in second that don't appear in first. 只會傳回唯一的元素。Only unique elements are returned.

Except<TSource>(IEnumerable<TSource>, IEnumerable<TSource>)

使用預設相等比較子來比較值,以便產生兩個序列的差異。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)

類型參數

TSource

輸入序列之項目的類型。The type of the elements of the input sequences.

參數

first
IEnumerable<TSource>

IEnumerable<T>,其項目若未同時存在 second 中,便會傳回這些項目。An IEnumerable<T> whose elements that are not also in second will be returned.

second
IEnumerable<TSource>

IEnumerable<T>,若其項目同時出現在第一個序列中,便會從傳回的序列中移除這些項目。An IEnumerable<T> whose elements that also occur in the first sequence will cause those elements to be removed from the returned sequence.

傳回

IEnumerable<TSource>

序列,其中包含兩個序列之項目的差異。A sequence that contains the set difference of the elements of two sequences.

例外狀況

firstsecondnullfirst or second is null.

範例

下列程式碼範例示範如何使用 Except<TSource>(IEnumerable<TSource>, IEnumerable<TSource>) 方法來比較兩個數字序列,以及只出現在第一個序列中的傳回元素。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.
Console.WriteLine(output.ToString())

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

如果您想要比較某些自訂資料類型的物件序列,就必須在 helper 類別中執行 IEquatable<T> 泛型介面。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. 下列程式碼範例示範如何在自訂資料類型中執行此介面,並覆寫 GetHashCodeEquals 方法。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

在您執行此介面之後,您可以在 Except<TSource>(IEnumerable<TSource>, IEnumerable<TSource>) 方法中使用 ProductA 物件的序列,如下列範例所示: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

備註

這個方法是使用延後執行來執行。This method is implemented by using deferred execution. 立即傳回值是一個物件,它會儲存執行動作所需的所有資訊。The immediate return value is an object that stores all the information that is required to perform the action. 在列舉物件之前,不會執行此方法所代表的查詢,方法是直接呼叫其 GetEnumerator 方法,或是在 Visual Basic 中C#使用 Visual 或 For Each 中的 foreachThe 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.

預設的相等比較子(Default)是用來比較類型的值。The default equality comparer, Default, is used to compare values of the types. 若要比較自訂資料類型,您必須覆寫 EqualsGetHashCode 方法,並選擇性地在自訂類型中執行 IEquatable<T> 泛型介面。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. 如需詳細資訊,請參閱 Default 屬性。For more information, see the Default property.

Except<TSource>(IEnumerable<TSource>, IEnumerable<TSource>, IEqualityComparer<TSource>)

使用指定的 IEqualityComparer<T> 來比較值,以便產生兩個序列的差異。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)

類型參數

TSource

輸入序列之項目的類型。The type of the elements of the input sequences.

參數

first
IEnumerable<TSource>

IEnumerable<T>,其項目若未同時存在 second 中,便會傳回這些項目。An IEnumerable<T> whose elements that are not also in second will be returned.

second
IEnumerable<TSource>

IEnumerable<T>,若其項目同時出現在第一個序列中,便會從傳回的序列中移除這些項目。An IEnumerable<T> whose elements that also occur in the first sequence will cause those elements to be removed from the returned sequence.

comparer
IEqualityComparer<TSource>

用來比較值的 IEqualityComparer<T>An IEqualityComparer<T> to compare values.

傳回

IEnumerable<TSource>

序列,其中包含兩個序列之項目的差異。A sequence that contains the set difference of the elements of two sequences.

例外狀況

firstsecondnullfirst or second is null.

範例

如果您想要比較某些自訂資料類型的物件序列,就必須在 helper 類別中執行 IEqualityComparer<T> 泛型介面。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. 下列程式碼範例示範如何在自訂資料類型中執行此介面,並提供 GetHashCodeEquals 方法。The following code example shows how to implement this interface in a custom data type and provide GetHashCode and Equals methods. 下列範例顯示如何執行可用於 Except 方法中的相等比較子。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

在您執行此比較子之後,您可以在 Except 方法中使用 Product 物件的序列,如下列範例所示: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

備註

如果 null``comparer,則會使用預設的相等比較子(Default)來比較值。If comparer is null, the default equality comparer, Default, is used to compare values.

適用於