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Enumerable.Union(TSource) Method (IEnumerable(TSource), IEnumerable(TSource))

Updated: October 2008

Produces the union of two sequences by using the default equality comparer.

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

JScript does not support generic types or methods.

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.

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).

ExceptionCondition
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.

This method excludes duplicates from the return set. This is different behavior to the Concat(TSource) 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(T) 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.

The following code example demonstrates how to use Union(TSource)(IEnumerable(TSource), IEnumerable(TSource)) to obtain the union of two sequences of integers.

No code example is currently available or this language may not be supported.

If you want to compare sequences of objects of a custom data type, you have to implement the IEqualityComparer(T) generic interface in the class. The following code example shows how to implement this interface in a custom data type and provide GetHashCode and Equals methods.

No code example is currently available or this language may not be supported.

After you implement this interface, you can use sequences of Product objects in the Union(TSource)(IEnumerable(TSource), IEnumerable(TSource)) method, as shown in the following example.

No code example is currently available or this language may not be supported.

Windows 7, Windows Vista, Windows XP SP2, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5

.NET Compact Framework

Supported in: 3.5

XNA Framework

Supported in: 3.0

Date

History

Reason

October 2008

Added more examples.

Customer feedback.

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