Enumerable.Union Method (System.Linq) (original) (raw)
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Produces the set union of two sequences by using the default equality comparer.
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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)Type Parameters
TSource
The type of the elements of the input sequences.
Parameters
Returns
An IEnumerable that contains the elements from both input sequences, excluding duplicates.
Exceptions
Examples
The following code example demonstrates how to use Union<TSource>(IEnumerable<TSource>, IEnumerable<TSource>) to obtain the union of two sequences of integers.
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
If you want to compare sequences of objects of some custom data type, you have to implement the IEquatable generic interface in a helper class. The following code example shows how to implement this interface in a custom data type and override GetHashCode and Equals methods.
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
After you implement this interface, you can use sequences of ProductA objects in the Union<TSource>(IEnumerable<TSource>, IEnumerable<TSource>) method, as shown in the following example:
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
'
Remarks
This method is implemented by using deferred execution. The immediate return value is an object that stores all the information that is required to perform the action. 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 C# or For Each in Visual Basic.
This method excludes duplicates from the return set. This is different behavior to the Concat method, which returns all the elements in the input sequences including duplicates.
The default equality comparer, Default, is used to compare values of the types that implement the IEqualityComparer generic interface. To compare a custom data type, you need to implement this interface and provide your own GetHashCode and Equals methods for the type.
When the object returned by this method is enumerated, Union enumerates first and second in that order and yields each element that has not already been yielded.