Enumerable.Concat<TSource> Method
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Concatenates two sequences.
Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)
Syntax
'Declaration
<ExtensionAttribute> _
Public Shared Function Concat(Of TSource) ( _
first As IEnumerable(Of TSource), _
second As IEnumerable(Of TSource) _
) As IEnumerable(Of TSource)
public static IEnumerable<TSource> Concat<TSource>(
this IEnumerable<TSource> first,
IEnumerable<TSource> second
)
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.
Exceptions
| Exception | Condition |
|---|---|
| ArgumentNullException | first or second is nulla 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.
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.
Examples
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.
outputBlock.Text &= output.ToString() & vbCrLf
End Sub
' This code produces the following output:
'
' Barley
' Boots
' Whiskers
' Bounder
' Snoopy
' Fido
class Pet
{
public string Name { get; set; }
public int Age { get; set; }
}
static Pet[] GetCats()
{
Pet[] cats = { new Pet { Name="Barley", Age=8 },
new Pet { Name="Boots", Age=4 },
new Pet { Name="Whiskers", Age=1 } };
return cats;
}
static Pet[] GetDogs()
{
Pet[] dogs = { new Pet { Name="Bounder", Age=3 },
new Pet { Name="Snoopy", Age=14 },
new Pet { Name="Fido", Age=9 } };
return dogs;
}
public static void ConcatEx1()
{
Pet[] cats = GetCats();
Pet[] dogs = GetDogs();
IEnumerable<string> query =
cats.Select(cat => cat.Name).Concat(dogs.Select(dog => dog.Name));
foreach (string name in query)
{
outputBlock.Text += name + "\n";
}
}
// 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.
outputBlock.Text &= output.ToString() & vbCrLf
' This code produces the following output:
'
' Barley
' Boots
' Whiskers
' Bounder
' Snoopy
' Fido
Pet[] cats = GetCats();
Pet[] dogs = GetDogs();
IEnumerable<string> query =
new[] { cats.Select(cat => cat.Name), dogs.Select(dog => dog.Name) }
.SelectMany(name => name);
foreach (string name in query)
{
outputBlock.Text += name + "\n";
}
// This code produces the following output:
//
// Barley
// Boots
// Whiskers
// Bounder
// Snoopy
// Fido
Version Information
Silverlight
Supported in: 5, 4, 3
Silverlight for Windows Phone
Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0
XNA Framework
Supported in: Xbox 360, Windows Phone OS 7.0
Platforms
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.