.NET Framework Class Library
EnumerableSelectManyTSource, TResult Method (IEnumerableTSource, FuncTSource, IEnumerableTResult)

Projects each element of a sequence to an IEnumerableT and flattens the resulting sequences into one sequence.

Namespace:   System.Linq
Assembly:  System.Core (in System.Core.dll)
Syntax
<[%$TOPIC/bb534336_en-us_VS_110_2_0_0_0_0%]> _
Public Shared Function SelectMany(Of TSource, TResult) ( _
	source As [%$TOPIC/bb534336_en-us_VS_110_2_0_0_0_1%](Of TSource), _
	selector As [%$TOPIC/bb534336_en-us_VS_110_2_0_0_0_2%](Of TSource, [%$TOPIC/bb534336_en-us_VS_110_2_0_0_0_3%](Of TResult)) _
) As [%$TOPIC/bb534336_en-us_VS_110_2_0_0_0_4%](Of TResult)
public static [%$TOPIC/bb534336_en-us_VS_110_2_0_1_0_0%]<TResult> SelectMany<TSource, TResult>(
	this [%$TOPIC/bb534336_en-us_VS_110_2_0_1_0_1%]<TSource> source,
	[%$TOPIC/bb534336_en-us_VS_110_2_0_1_0_2%]<TSource, [%$TOPIC/bb534336_en-us_VS_110_2_0_1_0_3%]<TResult>> selector
)
[[%$TOPIC/bb534336_en-us_VS_110_2_0_2_0_0%]]
public:
generic<typename TSource, typename TResult>
static [%$TOPIC/bb534336_en-us_VS_110_2_0_2_0_1%]<TResult>^ SelectMany(
	[%$TOPIC/bb534336_en-us_VS_110_2_0_2_0_2%]<TSource>^ source, 
	[%$TOPIC/bb534336_en-us_VS_110_2_0_2_0_3%]<TSource, [%$TOPIC/bb534336_en-us_VS_110_2_0_2_0_4%]<TResult>^>^ selector
)
static member SelectMany : 
        source:[%$TOPIC/bb534336_en-us_VS_110_2_0_3_0_0%]<'TSource> * 
        selector:[%$TOPIC/bb534336_en-us_VS_110_2_0_3_0_1%]<'TSource, [%$TOPIC/bb534336_en-us_VS_110_2_0_3_0_2%]<'TResult>> -> [%$TOPIC/bb534336_en-us_VS_110_2_0_3_0_3%]<'TResult> 
JScript does not support generic types or methods.

Type Parameters

TSource

The type of the elements of source.

TResult

The type of the elements of the sequence returned by selector.

Parameters

source
Type: System.Collections.GenericIEnumerableTSource

A sequence of values to project.

selector
Type: SystemFuncTSource, IEnumerableTResult

A transform function to apply to each element.

Return Value

Type: System.Collections.GenericIEnumerableTResult
An IEnumerableT whose elements are the result of invoking the one-to-many transform function on each element of the input sequence.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerableTSource. 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).
Exceptions
ExceptionCondition
ArgumentNullException

source or selector is .

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 SelectManyTSource, TResult(IEnumerableTSource, FuncTSource, IEnumerableTResult) method enumerates the input sequence, uses a transform function to map each element to an IEnumerableT, and then enumerates and yields the elements of each such IEnumerableT object. That is, for each element of source, selector is invoked and a sequence of values is returned. SelectManyTSource, TResult(IEnumerableTSource, FuncTSource, IEnumerableTResult) then flattens this two-dimensional collection of collections into a one-dimensional IEnumerableT and returns it. For example, if a query uses SelectManyTSource, TResult(IEnumerableTSource, FuncTSource, IEnumerableTResult) to obtain the orders (of type Order) for each customer in a database, the result is of type IEnumerable<Order> in C# or IEnumerable(Of Order) in Visual Basic. If instead the query uses Select to obtain the orders, the collection of collections of orders is not combined and the result is of type IEnumerable<List<Order>> in C# or IEnumerable(Of List(Of Order)) in Visual Basic.

In query expression syntax, each from clause (Visual C#) or From clause (Visual Basic) after the initial one translates to an invocation of SelectMany.

Examples

The following code example demonstrates how to use SelectManyTSource, TResult(IEnumerableTSource, FuncTSource, IEnumerableTResult) to perform a one-to-many projection over an array.

Structure PetOwner
        Public Name As String 
        Public Pets() As String 
    End Structure 

    Sub SelectManyEx1()
        ' Create an array of PetOwner objects. 
        Dim petOwners() As PetOwner = _
            {New PetOwner With _
             {.Name = "Higa, Sidney", .Pets = New String() {"Scruffy", "Sam"}}, _
             New PetOwner With _
             {.Name = "Ashkenazi, Ronen", .Pets = New String() {"Walker", "Sugar"}}, _
             New PetOwner With _
             {.Name = "Price, Vernette", .Pets = New String() {"Scratches", "Diesel"}}}

        ' Call SelectMany() to gather all pets into a "flat" sequence. 
        Dim query1 As IEnumerable(Of String) = _
            petOwners.SelectMany(Function(petOwner) petOwner.Pets)

        Dim output As New System.Text.StringBuilder("Using SelectMany():" & vbCrLf)
        ' Only one foreach loop is required to iterate through  
        ' the results because it is a one-dimensional collection. 
        For Each pet As String In query1
            output.AppendLine(pet)
        Next 

        ' This code demonstrates how to use Select() instead  
        ' of SelectMany() to get the same result. 
        Dim query2 As IEnumerable(Of String()) = _
            petOwners.Select(Function(petOwner) petOwner.Pets)
        output.AppendLine(vbCrLf & "Using Select():")
        ' Notice that two foreach loops are required to iterate through  
        ' the results because the query returns a collection of arrays. 
        For Each petArray() As String In query2
            For Each pet As String In petArray
                output.AppendLine(pet)
            Next 
        Next 

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

    ' This code produces the following output: 
    ' 
    ' Using SelectMany(): 
    ' Scruffy 
    ' Sam 
    ' Walker 
    ' Sugar 
    ' Scratches 
    ' Diesel 
    ' 
    ' Using Select(): 
    ' Scruffy 
    ' Sam 
    ' Walker 
    ' Sugar 
    ' Scratches 
    ' Diesel
class PetOwner
            {
                public string Name { get; set; }
                public List<String> Pets { get; set; }
            }

            public static void SelectManyEx1()
            {
                PetOwner[] petOwners = 
                    { new PetOwner { Name="Higa, Sidney", 
                          Pets = new List<string>{ "Scruffy", "Sam" } },
                      new PetOwner { Name="Ashkenazi, Ronen", 
                          Pets = new List<string>{ "Walker", "Sugar" } },
                      new PetOwner { Name="Price, Vernette", 
                          Pets = new List<string>{ "Scratches", "Diesel" } } };

                // Query using SelectMany().
                IEnumerable<string> query1 = petOwners.SelectMany(petOwner => petOwner.Pets);

                Console.WriteLine("Using SelectMany():");

                // Only one foreach loop is required to iterate  
                // through the results since it is a 
                // one-dimensional collection. 
                foreach (string pet in query1)
                {
                    Console.WriteLine(pet);
                }

                // This code shows how to use Select()  
                // instead of SelectMany().
                IEnumerable<List<String>> query2 =
                    petOwners.Select(petOwner => petOwner.Pets);

                Console.WriteLine("\nUsing Select():");

                // Notice that two foreach loops are required to  
                // iterate through the results 
                // because the query returns a collection of arrays. 
                foreach (List<String> petList in query2)
                {
                    foreach (string pet in petList)
                    {
                        Console.WriteLine(pet);
                    }
                    Console.WriteLine();
                }
            }

            /*
             This code produces the following output:

             Using SelectMany():
             Scruffy
             Sam
             Walker
             Sugar
             Scratches
             Diesel

             Using Select():
             Scruffy
             Sam

             Walker
             Sugar

             Scratches
             Diesel
            */
Version Information

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8