Enumerable.Distinct 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。

從序列傳回獨特的項目。

多載

Distinct<TSource>(IEnumerable<TSource>, IEqualityComparer<TSource>)	使用指定的 IEqualityComparer<T> 來比較值，以便從序列傳回獨特的項目。
Distinct<TSource>(IEnumerable<TSource>)	使用預設的相等比較子來比較值，以便從序列傳回獨特的項目。

備註

結果序列未排序。

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

來源:: Distinct.cs

來源:: Distinct.cs

來源:: Distinct.cs

使用指定的 IEqualityComparer<T> 來比較值，以便從序列傳回獨特的項目。

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

public static System.Collections.Generic.IEnumerable<TSource> Distinct<TSource> (this System.Collections.Generic.IEnumerable<TSource> source, System.Collections.Generic.IEqualityComparer<TSource> comparer);

public static System.Collections.Generic.IEnumerable<TSource> Distinct<TSource> (this System.Collections.Generic.IEnumerable<TSource> source, System.Collections.Generic.IEqualityComparer<TSource>? comparer);

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

<Extension()>
Public Function Distinct(Of TSource) (source As IEnumerable(Of TSource), comparer As IEqualityComparer(Of TSource)) As IEnumerable(Of TSource)

類型參數

TSource

source 項目的類型。

參數

source: IEnumerable<TSource>

要移除重複項目的序列。

comparer: IEqualityComparer<TSource>

用來比較值的 IEqualityComparer<T>。

傳回

IEnumerable<TSource>

IEnumerable<T>，其中包含來源序列中的獨特項目。

例外狀況

ArgumentNullException

source 為 null。

範例

下列範例示範如何實作可用於方法的 Distinct 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Distinct物件序列Product，如下列範例所示：

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

// Exclude duplicates.

IEnumerable<Product> noduplicates =
    products.Distinct(new ProductComparer());

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

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


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

' Exclude duplicates.

Dim noduplicates = products.Distinct(New ProductComparer())

For Each product In noduplicates
    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實作。立即傳回值是一個物件，會儲存執行動作所需的所有資訊。除非直接呼叫其 GetEnumerator 方法或在 C# 或 foreachFor Each Visual Basic 中使用來列舉對象，否則不會執行這個方法所代表的查詢。

方法 Distinct<TSource>(IEnumerable<TSource>, IEqualityComparer<TSource>) 會傳回不含重複值的未排序序列。如果為 comparernull，則會使用預設相等比較子 Default來比較值。

適用於

Distinct<TSource>(IEnumerable<TSource>)

來源:: Distinct.cs

來源:: Distinct.cs

來源:: Distinct.cs

使用預設的相等比較子來比較值，以便從序列傳回獨特的項目。

public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::IEnumerable<TSource> ^ Distinct(System::Collections::Generic::IEnumerable<TSource> ^ source);

public static System.Collections.Generic.IEnumerable<TSource> Distinct<TSource> (this System.Collections.Generic.IEnumerable<TSource> source);

static member Distinct : seq<'Source> -> seq<'Source>

<Extension()>
Public Function Distinct(Of TSource) (source As IEnumerable(Of TSource)) As IEnumerable(Of TSource)

類型參數

TSource

source 項目的類型。

參數

source: IEnumerable<TSource>

要移除重複項目的序列。

傳回

IEnumerable<TSource>

IEnumerable<T>，其中包含來源序列中的獨特項目。

例外狀況

ArgumentNullException

source 為 null。

範例

下列程式代碼範例示範如何使用 Distinct<TSource>(IEnumerable<TSource>) 從整數序列傳回不同的專案。

List<int> ages = new List<int> { 21, 46, 46, 55, 17, 21, 55, 55 };

IEnumerable<int> distinctAges = ages.Distinct();

Console.WriteLine("Distinct ages:");

foreach (int age in distinctAges)
{
    Console.WriteLine(age);
}

/*
 This code produces the following output:

 Distinct ages:
 21
 46
 55
 17
*/

' Create a list of integers.
Dim ages As New List(Of Integer)(New Integer() _
                             {21, 46, 46, 55, 17, 21, 55, 55})

' Select the unique numbers in the List.
Dim distinctAges As IEnumerable(Of Integer) = ages.Distinct()

Dim output As New System.Text.StringBuilder("Distinct ages:" & vbCrLf)
For Each age As Integer In distinctAges
    output.AppendLine(age)
Next

' Display the output.
Console.WriteLine(output.ToString)

' This code produces the following output:
'
' Distinct ages:
' 21
' 46
' 55
' 17

如果您想要從某些自定義數據類型的物件序列傳回不同的專案，則必須在類別中實 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，並提供 GetHashCode 和 Equals 方法。

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

    public bool Equals(MyProduct other)
    {
        //Check whether the compared object is null.
        if (Object.ReferenceEquals(other, null)) return false;

        //Check whether the compared object references the same data.
        if (Object.ReferenceEquals(this, other)) return true;

        //Check whether the products' properties are equal.
        return Code.Equals(other.Code) && Name.Equals(other.Name);
    }

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

    public override int GetHashCode()
    {

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

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

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

Public Class Product
    Implements IEquatable(Of Product)

    Public Property Name As String
    Public Property Code As Integer

    Public Function Equals1(
        ByVal other As Product
        ) As Boolean Implements IEquatable(Of Product).Equals

        ' Check whether the compared object is null.
        If other Is Nothing Then Return False

        ' Check whether the compared object references the same data.
        If Me Is Other Then Return True

        ' Check whether the products' properties are equal.
        Return Code.Equals(other.Code) AndAlso Name.Equals(other.Name)
    End Function

    Public Overrides Function GetHashCode() As Integer

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

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

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

實作此介面之後，您可以在方法中使用Distinct<TSource>(IEnumerable<TSource>)一連串Product的物件，如下列範例所示：

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

// Exclude duplicates.

IEnumerable<MyProduct> noduplicates =
    products.Distinct();

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

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


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

' Exclude duplicates.

Dim noduplicates = products.Distinct()

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

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

備註

方法 Distinct<TSource>(IEnumerable<TSource>) 會傳回不含重複值的未排序序列。它會使用預設相等比較子、 Default來比較值。

在 Visual Basic 查詢表達式語法中， Distinct 子句會轉譯為的 Distinct調用。

默認的相等比較子 Default是用來比較實 IEquatable<T> 作泛型介面之型別的值。若要比較自定義數據類型，您必須實作此介面，並提供您自己的 GetHashCode 和 Equals 方法給類型。

如需使用 IEqualityComparer<T> 來定義自訂比較子的範例，請參閱 Distinct<TSource>(IEnumerable<TSource>, IEqualityComparer<TSource>)。

另請參閱

Distinct 子句 (Visual Basic)

適用於

共用方式為

Enumerable.Distinct 方法

定義

多載

備註

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

類型參數

參數

傳回

例外狀況

範例

備註

適用於

Distinct<TSource>(IEnumerable<TSource>)

類型參數

參數

傳回

例外狀況

範例

備註

另請參閱

適用於

其他資源