Enumerable.Union<(Of <(TSource>)>) Method (IEnumerable<(Of <(TSource>)>), IEnumerable<(Of <(TSource>)>), IEqualityComparer<(Of <(TSource>)>))

[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]

Produces the set union of two sequences by using a specified IEqualityComparer<(Of <(T>)>).

Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)

Syntax

<ExtensionAttribute> _
Public Shared Function Union(Of TSource) ( _
    first As IEnumerable(Of TSource), _
    second As IEnumerable(Of TSource), _
    comparer As IEqualityComparer(Of TSource) _
) As IEnumerable(Of TSource)
public static IEnumerable<TSource> Union<TSource>(
    this IEnumerable<TSource> first,
    IEnumerable<TSource> second,
    IEqualityComparer<TSource> comparer
)

Type Parameters

  • TSource
    The type of the elements of the input sequences.

Parameters

Return Value

Type: System.Collections.Generic..::.IEnumerable<(Of <(TSource>)>)
An IEnumerable<(Of <(T>)>) that contains the elements from both input sequences, excluding duplicates.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable<(Of <(TSource>)>). When you use instance method syntax to call this method, omit the first parameter.

Exceptions

Exception Condition
ArgumentNullException

first or second is nullNothingnullptra null reference (Nothing in Visual Basic).

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 Visual C# or For Each in Visual Basic.

If comparer is nullNothingnullptra null reference (Nothing in Visual Basic), the default equality comparer, Default, is used to compare values.

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.

The Concat<(Of <(TSource>)>) method differs from the Union method because the Concat<(Of <(TSource>)>) method returns all the elements in the input sequences including duplicates, whereas Union returns only unique values.

Version Information

Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Platforms

Windows Phone

See Also

Reference

Enumerable Class

Union Overload

System.Linq Namespace