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Enumerable.Concat<TSource> Method

Concatenates two sequences.

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

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.

ExceptionCondition
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.


      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.


         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



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

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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