Enumerable.Except 方法

參考

定義

命名空間:: System.Linq

組件:: System.Linq.dll

組件:: System.Core.dll

組件:: netstandard.dll

重要

部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。

產生兩個序列的差異。

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。
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。

備註

兩組集合的集合差異會定義為第一個集合的成員，而該集合不會出現在第二個集合中。

這個方法會傳回中未出現在中的firstsecond專案。它不會傳回中未出現在中的secondfirst專案。只會傳回唯一的專案。

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

來源:: Except.cs

來源:: Except.cs

來源:: Except.cs

使用預設相等比較子來比較值，以便產生兩個序列的差異。

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。

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。

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。

傳回

IEnumerable<TSource>

序列，其中包含兩個序列之項目的差異。

例外狀況

ArgumentNullException

first 或 second 為 null。

範例

下列程式代碼範例示範如何使用 Except<TSource>(IEnumerable<TSource>, IEnumerable<TSource>) 方法來比較兩個數位序列，並傳回只出現在第一個序列中的元素。

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定義資料類型的物件序列，您必須在協助程序類別中實 IEquatable<T> 作泛型介面。下列程式代碼範例示範如何在自定義數據類型中實作此介面，並覆寫 GetHashCode 和 Equals 方法。

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

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

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

此方法是使用延後執行來實作。立即傳回值是物件，可儲存執行動作所需的所有資訊。除非直接在 GetEnumerator C# 或 Visual Basic 中使用 foreach 來列舉對象，否則 For Each 不會執行這個方法所表示的查詢。

默認相等比較子 Default是用來比較型別的值。若要比較自定義數據類型，您必須覆寫 Equals 和 GetHashCode 方法，並選擇性地在自定義類型中實 IEquatable<T> 作泛型介面。如需詳細資訊，請參閱 Default 屬性 (Property)。

適用於

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

來源:: Except.cs

來源:: Except.cs

來源:: Except.cs

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

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);

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。

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。

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。

comparer: IEqualityComparer<TSource>

用來比較值的 IEqualityComparer<T>。

傳回

IEnumerable<TSource>

序列，其中包含兩個序列之項目的差異。

例外狀況

ArgumentNullException

first 或 second 為 null。

範例

如果您想要比較某些自定義資料類型的物件序列，您必須在協助程序類別中實 IEqualityComparer<T> 作泛型介面。下列程式代碼範例示範如何在自定義數據類型中實作此介面，並提供 GetHashCode 和 Equals 方法。下列範例示範如何實作方法中 Except 可使用的相等比較子。

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

實作這個比較子之後，您可以在方法中使用Except物件的序列Product，如下列範例所示：

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 comparer 為 null，則會使用預設相等比較子 Default來比較值。

適用於

共用方式為

Enumerable.Except 方法

定義

多載

備註

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

類型參數

參數

傳回

例外狀況

範例

備註

適用於

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

類型參數

參數

傳回

例外狀況

範例

備註

適用於

其他資源