Enumerable.Union Method

Definition

 Union(IEnumerable, IEnumerable) 通过使用默认的相等比较器，生成两个序列的并集。Produces the set union of two sequences by using the default equality comparer. Union(IEnumerable, IEnumerable, IEqualityComparer) 通过使用指定的 IEqualityComparer 生成两个序列的并集。Produces the set union of two sequences by using a specified IEqualityComparer.

Union<TSource>(IEnumerable<TSource>, IEnumerable<TSource>)

``````public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
static System::Collections::Generic::IEnumerable<TSource> ^ Union(System::Collections::Generic::IEnumerable<TSource> ^ first, System::Collections::Generic::IEnumerable<TSource> ^ second);``````
``public static System.Collections.Generic.IEnumerable<TSource> Union<TSource> (this System.Collections.Generic.IEnumerable<TSource> first, System.Collections.Generic.IEnumerable<TSource> second);``
``static member Union : seq<'Source> * seq<'Source> -> seq<'Source>``
``````<Extension()>
Public Function Union(Of TSource) (first As IEnumerable(Of TSource), second As IEnumerable(Of TSource)) As IEnumerable(Of TSource)``````

TSource

Parameters

first
IEnumerable<TSource>

second
IEnumerable<TSource>

Returns

IEnumerable<TSource>

Exceptions

`first``second``null``first` or `second` is `null`.

Examples

``````int[] ints1 = { 5, 3, 9, 7, 5, 9, 3, 7 };
int[] ints2 = { 8, 3, 6, 4, 4, 9, 1, 0 };

IEnumerable<int> union = ints1.Union(ints2);

foreach (int num in union)
{
Console.Write("{0} ", num);
}

/*
This code produces the following output:

5 3 9 7 8 6 4 1 0
*/
``````
``````' Create two arrays of integer values.
Dim ints1() As Integer = {5, 3, 9, 7, 5, 9, 3, 7}
Dim ints2() As Integer = {8, 3, 6, 4, 4, 9, 1, 0}

' Get the set union of the two arrays.
Dim union As IEnumerable(Of Integer) = ints1.Union(ints2)

' Display the resulting set's values.
Dim output As New System.Text.StringBuilder
For Each num As Integer In union
output.AppendLine(num & " ")
Next
Console.WriteLine(output.ToString())

' This code produces the following output:
'
' 5
' 3
' 9
' 7
' 8
' 6
' 4
' 1
' 0
``````

``````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
``````

``````ProductA[] store1 = { new ProductA { Name = "apple", Code = 9 },
new ProductA { Name = "orange", Code = 4 } };

ProductA[] store2 = { new ProductA { Name = "apple", Code = 9 },
new ProductA { Name = "lemon", Code = 12 } };
``````
``````Dim store1() As ProductA =
{New Product With {.Name = "apple", .Code = 9},
New Product With {.Name = "orange", .Code = 4}}

Dim store2() As ProductA =
{New Product With {.Name = "apple", .Code = 9},
New Product With {.Name = "lemon", .Code = 12}}
``````
``````//Get the products from the both arrays
//excluding duplicates.

IEnumerable<ProductA> union =
store1.Union(store2);

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

/*
This code produces the following output:

apple 9
orange 4
lemon 12
*/
``````
``````' Get the products from the both arrays
' excluding duplicates.

Dim union = store1.Union(store2)

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

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

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

``````public:
generic <typename TSource>
[System::Runtime::CompilerServices::Extension]
static System::Collections::Generic::IEnumerable<TSource> ^ Union(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> Union<TSource> (this System.Collections.Generic.IEnumerable<TSource> first, System.Collections.Generic.IEnumerable<TSource> second, System.Collections.Generic.IEqualityComparer<TSource> comparer);``
``static member Union : seq<'Source> * seq<'Source> * System.Collections.Generic.IEqualityComparer<'Source> -> seq<'Source>``
``````<Extension()>
Public Function Union(Of TSource) (first As IEnumerable(Of TSource), second As IEnumerable(Of TSource), comparer As IEqualityComparer(Of TSource)) As IEnumerable(Of TSource)``````

TSource

Parameters

first
IEnumerable<TSource>

second
IEnumerable<TSource>

comparer
IEqualityComparer<TSource>

Returns

IEnumerable<TSource>

Exceptions

`first``second``null``first` or `second` is `null`.

Examples

``````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
``````

``````Product[] store1 = { new Product { Name = "apple", Code = 9 },
new Product { Name = "orange", Code = 4 } };

Product[] store2 = { new Product { Name = "apple", Code = 9 },
new Product { Name = "lemon", Code = 12 } };
``````
``````Dim store1() As Product =
{New Product With {.Name = "apple", .Code = 9},
New Product With {.Name = "orange", .Code = 4}}

Dim store2() As Product =
{New Product With {.Name = "apple", .Code = 9},
New Product With {.Name = "lemon", .Code = 12}}
``````
``````//Get the products from the both arrays
//excluding duplicates.

IEnumerable<Product> union =
store1.Union(store2, new ProductComparer());

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

/*
This code produces the following output:

apple 9
orange 4
lemon 12
*/
``````
``````' Get the products from the both arrays
' excluding duplicates.

Dim union = store1.Union(store2, New ProductComparer())

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

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

Remarks

Concat 方法不同于 Union 方法，因为 Concat 方法返回输入序列中的所有元素（包括重复项），而 Union 仅返回唯一值。The Concat method differs from the Union method because the Concat method returns all the elements in the input sequences including duplicates, whereas Union returns only unique values.