Duration (Pacific Standard Time):
To (Pacific Standard Time):
Impact:
  • None
User Action:
  • None
.NET Framework Class Library

Enumerable.Concat<TSource> Method

Concatenates two sequences.

Namespace:  System.Linq
Assembly:  System.Core (in System.Core.dll)
<ExtensionAttribute> _
Public Shared Function Concat(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

first
Type: System.Collections.Generic.IEnumerable<TSource>

The first sequence to concatenate.

second
Type: System.Collections.Generic.IEnumerable<TSource>

The sequence to concatenate to the first sequence.

Return Value

Type: System.Collections.Generic.IEnumerable<TSource>
An IEnumerable<T> that contains the concatenated elements of the two input sequences.

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 null.

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.

The Concat<TSource>(IEnumerable<TSource>, IEnumerable<TSource>) method differs from the Union method because the Concat<TSource>(IEnumerable<TSource>, IEnumerable<TSource>) method returns all the original elements in the input sequences. The Union method returns only unique elements.

The following code example demonstrates how to use Concat<TSource>(IEnumerable<TSource>, IEnumerable<TSource>) to concatenate two sequences.

    Structure Pet
        Public Name As String 
        Public Age As Integer 
    End Structure 

    ' Returns an array of Pet objects. 
    Function GetCats() As Pet()
        Dim cats() As Pet = {New Pet With {.Name = "Barley", .Age = 8}, _
                             New Pet With {.Name = "Boots", .Age = 4}, _
                             New Pet With {.Name = "Whiskers", .Age = 1}}

        Return cats
    End Function 

    ' Returns an array of Pet objects. 
    Function GetDogs() As Pet()
        Dim dogs() As Pet = {New Pet With {.Name = "Bounder", .Age = 3}, _
                             New Pet With {.Name = "Snoopy", .Age = 14}, _
                             New Pet With {.Name = "Fido", .Age = 9}}
        Return dogs
    End Function 

    Sub ConcatEx1()
        ' Create two arrays of Pet objects. 
        Dim cats() As Pet = GetCats()
        Dim dogs() As Pet = GetDogs()

        ' Project the Name of each cat and concatenate 
        ' the collection of cat name strings with a collection 
        ' of dog name strings. 
        Dim query As IEnumerable(Of String) = _
            cats _
            .Select(Function(cat) cat.Name) _
            .Concat(dogs.Select(Function(dog) dog.Name))

        Dim output As New System.Text.StringBuilder
        For Each name As String In query
            output.AppendLine(name)
        Next 

        ' Display the output.
        MsgBox(output.ToString())
    End Sub 

    ' This code produces the following output: 
    
    ' Barley 
    ' Boots 
    ' Whiskers 
    ' Bounder 
    ' Snoopy 
    ' Fido

An alternative way of concatenating two sequences is to construct a collection, for example an array, of sequences and then apply the SelectMany method, passing it the identity selector function. The following example demonstrates this use of SelectMany.

        ' Create two arrays of Pet objects. 
        Dim cats() As Pet = GetCats()
        Dim dogs() As Pet = GetDogs()

        ' Create an IEnumerable collection that contains two elements. 
        ' Each element is an array of Pet objects. 
        Dim animals() As IEnumerable(Of Pet) = {cats, dogs}

        Dim query As IEnumerable(Of String) = _
            (animals.SelectMany(Function(pets) _
                                    pets.Select(Function(pet) pet.Name)))

        Dim output As New System.Text.StringBuilder
        For Each name As String In query
            output.AppendLine(name)
        Next 

        ' Display the output.
        MsgBox(output.ToString())

        ' This code produces the following output: 
        
        ' Barley 
        ' Boots 
        ' Whiskers 
        ' Bounder 
        ' Snoopy 
        ' Fido

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, 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.