Enumerable.Except 方法

参考

定义

命名空间:: System.Linq

程序集:: System.Linq.dll

程序集:: System.Core.dll

程序集:: netstandard.dll

重要

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生成两个序列的差集。

重载

Except<TSource>(IEnumerable<TSource>, IEnumerable<TSource>)	通过使用默认的相等比较器对值进行比较，生成两个序列的差集。
Except<TSource>(IEnumerable<TSource>, IEnumerable<TSource>, IEqualityComparer<TSource>)	通过使用指定的 IEqualityComparer<T> 对值进行比较，生成两个序列的差集。

注解

两个集的集差定义为第二个集中未显示的第一个集的成员。

此方法返回中 first 未显示在中的 second那些元素。它不会返回中 second 未显示在中的 first那些元素。仅返回唯一元素。

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

Source:: Except.cs

Source:: Except.cs

Source:: Except.cs

通过使用默认的相等比较器对值进行比较，生成两个序列的差集。

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)

类型参数

TSource

输入序列中的元素的类型。

参数

first: IEnumerable<TSource>

一个 IEnumerable<T>，将返回其不在 second 中的元素。

second: IEnumerable<TSource>

一个 IEnumerable<T>，其中的元素如果同时出现在第一个序列中，则将导致从返回的序列中移除这些元素。

IEnumerable<TSource>

包含这两个序列的元素的差集的序列。

例外

ArgumentNullException

first 或 second 为 null。

示例

下面的代码示例演示如何使用 Except<TSource>(IEnumerable<TSource>, IEnumerable<TSource>) 方法比较两个数字序列，并返回仅出现在第一个序列中的元素。

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

如果要比较某些自定义数据类型的对象序列，则必须在帮助程序类中实现 IEquatable<T> 泛型接口。下面的代码示例演示如何在自定义数据类型中实现此接口并重写 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

实现此接口后，可以在方法中使用Except<TSource>(IEnumerable<TSource>, IEnumerable<TSource>)对象的序列ProductA，如以下示例所示：

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

注解

此方法通过使用延迟执行来实现。即时返回值是一个对象，用于存储执行操作所需的所有信息。在通过直接调用GetEnumerator其方法或通过在 C# For Each 或 foreach Visual Basic 中使用来枚举对象之前，不会执行此方法表示的查询。

默认相等比较器 Default用于比较类型的值。若要比较自定义数据类型，需要重写 Equals 和 GetHashCode 方法，并选择性地在自定义类型中实现 IEquatable<T> 泛型接口。有关更多信息，请参见 Default 属性。

适用于

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

Source:: Except.cs

Source:: Except.cs

Source:: Except.cs

通过使用指定的 IEqualityComparer<T> 对值进行比较，生成两个序列的差集。

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)

类型参数

TSource

输入序列中的元素的类型。

参数

first: IEnumerable<TSource>

一个 IEnumerable<T>，将返回其不在 second 中的元素。

second: IEnumerable<TSource>

一个 IEnumerable<T>，其中的元素如果同时出现在第一个序列中，则将导致从返回的序列中移除这些元素。

comparer: IEqualityComparer<TSource>

用于比较值的 IEqualityComparer<T>。

IEnumerable<TSource>

包含这两个序列的元素的差集的序列。

例外

ArgumentNullException

first 或 second 为 null。

示例

如果要比较某些自定义数据类型的对象序列，则必须在帮助程序类中实现 IEqualityComparer<T> 泛型接口。下面的代码示例演示如何在自定义数据类型中实现此接口，并提供 GetHashCode 和 Equals 方法。以下示例演示如何实现可在方法中使用的 Except 相等比较器。

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

实现此比较器后，可以在方法中使用Except对象的序列Product，如以下示例所示：

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

注解

如果 comparer 为 null，则使用默认相等比较器 Default来比较值。

适用于

Enumerable.Except 方法

定义

重载

注解

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

类型参数

参数

返回

例外

示例

注解

适用于

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

类型参数

参数

返回

例外

示例

注解

适用于

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