Enumerable.Union(TSource) Method (IEnumerable(TSource), IEnumerable(TSource), IEqualityComparer(TSource))
Produces the set union of two sequences by using a specified IEqualityComparer(T).
Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)
static member Union : first:IEnumerable<'TSource> * second:IEnumerable<'TSource> * comparer:IEqualityComparer<'TSource> -> IEnumerable<'TSource>
Type Parameters
- TSource
The type of the elements of the input sequences.
Parameters
- first
- Type: System.Collections.Generic.IEnumerable(TSource)
An IEnumerable(T) whose distinct elements form the first set for the union.
- second
- Type: System.Collections.Generic.IEnumerable(TSource)
An IEnumerable(T) whose distinct elements form the second set for the union.
- comparer
- Type: System.Collections.Generic.IEqualityComparer(TSource)
The IEqualityComparer(T) to compare values.
Return Value
Type: System.Collections.Generic.IEnumerable(TSource)An IEnumerable(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(TSource). When you use instance method syntax to call this method, omit the first parameter. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).| Exception | Condition |
|---|---|
| ArgumentNullException | first or second is a null reference (Nothing in Visual Basic). |
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 a 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(TSource) method differs from the Union method because the Concat(TSource) method returns all the elements in the input sequences including duplicates, whereas Union returns only unique values.
Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
