Enumerable.Union(TSource) Method (IEnumerable(TSource), IEnumerable(TSource))
Updated: October 2008
Produces the union of two sequences by using the default equality comparer.
Assembly: System.Core (in System.Core.dll)
The type of the elements of the input sequences.
- Type: System.Collections.Generic.IEnumerable()
An IEnumerable(T) whose distinct elements form the first set for the union.
Return ValueType: System.Collections.Generic.IEnumerable()
An IEnumerable(T) that contains the elements from both input sequences, excluding duplicates.
Usage NoteIn Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable(). 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).
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 to obtain the union of two sequences of integers.
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.
After you implement this interface, you can use sequences of Product objects in the method, as shown in the following example.
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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.