Enumerable.Distinct Enumerable.Distinct Enumerable.Distinct Enumerable.Distinct Method

定義

從序列傳回獨特的項目。Returns distinct elements from a sequence.

多載

Distinct<TSource>(IEnumerable<TSource>) Distinct<TSource>(IEnumerable<TSource>) Distinct<TSource>(IEnumerable<TSource>) Distinct<TSource>(IEnumerable<TSource>)

使用預設相等比較子來比較值,從序列傳回獨特的項目。Returns distinct elements from a sequence by using the default equality comparer to compare values.

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

從序列傳回獨特的項目,使用指定的IEqualityComparer<T>來比較值。Returns distinct elements from a sequence by using a specified IEqualityComparer<T> to compare values.

備註

結果序列沒有排序。The result sequence is unordered.

Distinct<TSource>(IEnumerable<TSource>) Distinct<TSource>(IEnumerable<TSource>) Distinct<TSource>(IEnumerable<TSource>) Distinct<TSource>(IEnumerable<TSource>)

使用預設相等比較子來比較值,從序列傳回獨特的項目。Returns distinct elements from a sequence by using the default equality comparer to compare values.

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。The type of the elements of source.

參數

source
IEnumerable<TSource>

要移除重複項目的序列。The sequence to remove duplicate elements from.

傳回

IEnumerable<TSource>

IEnumerable<T>其中包含來源序列中的相異項目。An IEnumerable<T> that contains distinct elements from the source sequence.

例外狀況

範例

下列程式碼範例示範如何使用Distinct<TSource>(IEnumerable<TSource>)從整數的序列傳回獨特的項目。The following code example demonstrates how to use Distinct<TSource>(IEnumerable<TSource>) to return distinct elements from a sequence of integers.

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.
MsgBox(output.ToString)

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

如果您想要從某種自訂資料類型的物件序列傳回獨特的項目,您必須實作IEquatable<T>類別中的泛型介面。If you want to return distinct elements from sequences of objects of some custom data type, you have to implement the IEquatable<T> generic interface in the class. 下列程式碼範例示範如何實作這個介面中的自訂資料類型,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.

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

    public bool Equals(Product 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

您實作這個介面之後,您可以使用一連串Product中的物件Distinct<TSource>(IEnumerable<TSource>)方法,如下列範例所示:After you implement this interface, you can use a sequence of Product objects in the Distinct<TSource>(IEnumerable<TSource>) method, as shown in the following example:

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();

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

實作這個方法是使用延後的執行。This method is implemented by using deferred execution. 立即傳回值是儲存,才能執行此動作的所有資訊的物件。The immediate return value is an object that stores all the information that is required to perform the action. 這個方法所表示的查詢不會執行直到列舉物件可以藉由呼叫其GetEnumerator方法直接或透過foreachVisual C# 中或For EachVisual Basic 中。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.

Distinct<TSource>(IEnumerable<TSource>)方法會傳回未排序的序列,其中包含任何重複的值。The Distinct<TSource>(IEnumerable<TSource>) method returns an unordered sequence that contains no duplicate values. 它會使用預設相等比較子, Default,來比較值。It uses the default equality comparer, Default, to compare values.

在 Visual Basic 查詢運算式語法中,Distinct子句會轉譯成的引動過程DistinctIn Visual Basic query expression syntax, a Distinct clause translates to an invocation of Distinct.

預設相等比較子, Default,用來比較值的類型可實作IEquatable<T>泛型介面。The default equality comparer, Default, is used to compare values of the types that implement the IEquatable<T> generic interface. 若要比較的自訂資料類型,您需要實作這個介面,並提供您自己GetHashCodeEquals類型的方法。To compare a custom data type, you need to implement this interface and provide your own GetHashCode and Equals methods for the type.

如需使用的範例IEqualityComparer<T>若要定義自訂比較子,請參閱Distinct<TSource>(IEnumerable<TSource>, IEqualityComparer<TSource>)For an example that uses IEqualityComparer<T> to define a custom comparer, see Distinct<TSource>(IEnumerable<TSource>, IEqualityComparer<TSource>).

另請參閱

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

從序列傳回獨特的項目,使用指定的IEqualityComparer<T>來比較值。Returns distinct elements from a sequence by using a specified IEqualityComparer<T> to compare values.

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);
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。The type of the elements of source.

參數

source
IEnumerable<TSource>

要移除重複項目的序列。The sequence to remove duplicate elements from.

comparer
IEqualityComparer<TSource>

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

傳回

IEnumerable<TSource>

IEnumerable<T>其中包含來源序列中的相異項目。An IEnumerable<T> that contains distinct elements from the source sequence.

例外狀況

範例

下列範例示範如何實作可用於相等比較子Distinct方法。The following example shows how to implement an equality comparer that can be used in the Distinct 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

實作這個比較子之後,您可以使用一連串Product中的物件Distinct方法,如下列範例所示:After you implement this comparer, you can use a sequence of Product objects in the Distinct method, as shown in the following example:

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

實作這個方法是使用延後的執行。This method is implemented by using deferred execution. 立即傳回值是儲存,才能執行此動作的所有資訊的物件。The immediate return value is an object that stores all the information that is required to perform the action. 這個方法所表示的查詢不會執行直到列舉物件可以藉由呼叫其GetEnumerator方法直接或透過foreachVisual C# 中或For EachVisual Basic 中。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.

Distinct<TSource>(IEnumerable<TSource>, IEqualityComparer<TSource>)方法會傳回未排序的序列,其中包含任何重複的值。The Distinct<TSource>(IEnumerable<TSource>, IEqualityComparer<TSource>) method returns an unordered sequence that contains no duplicate values. 如果comparernull,預設的相等比較子, Default,用來比較值。If comparer is null, the default equality comparer, Default, is used to compare values.

適用於