Enumerable.SelectMany Enumerable.SelectMany Enumerable.SelectMany Enumerable.SelectMany Method

定義

每個序列的項目至IEnumerable<T>和壓平合併成單一序列產生的序列。Projects each element of a sequence to an IEnumerable<T> and flattens the resulting sequences into one sequence.

多載

SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>) SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>) SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>) SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>)

每個序列的項目至IEnumerable<T>壓平合併成單一序列,產生的序列,其中叫用結果選取器函式,每個項目。Projects each element of a sequence to an IEnumerable<T>, flattens the resulting sequences into one sequence, and invokes a result selector function on each element therein.

SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>) SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>) SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>) SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>)

每個序列的項目至IEnumerable<T>壓平合併成單一序列,產生的序列,其中叫用結果選取器函式,每個項目。Projects each element of a sequence to an IEnumerable<T>, flattens the resulting sequences into one sequence, and invokes a result selector function on each element therein. 各來源項目的索引是在該項目的中繼投影表單中使用。The index of each source element is used in the intermediate projected form of that element.

SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TResult>>) SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TResult>>) SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TResult>>) SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TResult>>)

每個序列的項目至IEnumerable<T>和壓平合併成單一序列產生的序列。Projects each element of a sequence to an IEnumerable<T> and flattens the resulting sequences into one sequence.

SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TResult>>) SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TResult>>) SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TResult>>) SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TResult>>)

每個序列的項目至IEnumerable<T>,並將簡化成單一序列產生的序列。Projects each element of a sequence to an IEnumerable<T>, and flattens the resulting sequences into one sequence. 各來源項目的索引是在該項目的投影表單中使用。The index of each source element is used in the projected form of that element.

SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>) SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>) SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>) SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>)

每個序列的項目至IEnumerable<T>壓平合併成單一序列,產生的序列,其中叫用結果選取器函式,每個項目。Projects each element of a sequence to an IEnumerable<T>, flattens the resulting sequences into one sequence, and invokes a result selector function on each element therein.

public:
generic <typename TSource, typename TCollection, typename TResult>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::IEnumerable<TResult> ^ SelectMany(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, System::Collections::Generic::IEnumerable<TCollection> ^> ^ collectionSelector, Func<TSource, TCollection, TResult> ^ resultSelector);
public static System.Collections.Generic.IEnumerable<TResult> SelectMany<TSource,TCollection,TResult> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,System.Collections.Generic.IEnumerable<TCollection>> collectionSelector, Func<TSource,TCollection,TResult> resultSelector);
static member SelectMany : seq<'Source> * Func<'Source, seq<'Collection>> * Func<'Source, 'Collection, 'Result> -> seq<'Result>
<Extension()>
Public Function SelectMany(Of TSource, TCollection, TResult) (source As IEnumerable(Of TSource), collectionSelector As Func(Of TSource, IEnumerable(Of TCollection)), resultSelector As Func(Of TSource, TCollection, TResult)) As IEnumerable(Of TResult)

類型參數

TSource

source 項目的類型。The type of the elements of source.

TCollection

所收集之中繼項目的型別collectionSelectorThe type of the intermediate elements collected by collectionSelector.

TResult

產生的序列的項目類型。The type of the elements of the resulting sequence.

參數

source
IEnumerable<TSource>

要投影的值序列。A sequence of values to project.

collectionSelector
Func<TSource,IEnumerable<TCollection>>

套用至輸入序列的每個項目的轉換函式。A transform function to apply to each element of the input sequence.

resultSelector
Func<TSource,TCollection,TResult>

若要套用到中繼序列各個項目的轉換函式。A transform function to apply to each element of the intermediate sequence.

傳回

IEnumerable<TResult>

IEnumerable<T>其項目是叫用來從一對多轉換函式的結果collectionSelector各項目上source然後再將每個序列項目及其對應的來源項目對應至結果項目。An IEnumerable<T> whose elements are the result of invoking the one-to-many transform function collectionSelector on each element of source and then mapping each of those sequence elements and their corresponding source element to a result element.

例外狀況

sourcecollectionSelectorresultSelectornullsource or collectionSelector or resultSelector is null.

範例

下列程式碼範例示範如何使用SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>)對陣列進行反覆執行的一對多投影,並使用結果選取器函式保留來源序列中最後一個呼叫的範圍中的每個對應的項目SelectThe following code example demonstrates how to use SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>) to perform a one-to-many projection over an array and use a result selector function to keep each corresponding element from the source sequence in scope for the final call to Select.

class PetOwner
{
    public string Name { get; set; }
    public List<string> Pets { get; set; }
}

public static void SelectManyEx3()
{
    PetOwner[] petOwners =
        { new PetOwner { Name="Higa", 
              Pets = new List<string>{ "Scruffy", "Sam" } },
          new PetOwner { Name="Ashkenazi", 
              Pets = new List<string>{ "Walker", "Sugar" } },
          new PetOwner { Name="Price", 
              Pets = new List<string>{ "Scratches", "Diesel" } },
          new PetOwner { Name="Hines", 
              Pets = new List<string>{ "Dusty" } } };

    // Project the pet owner's name and the pet's name.
    var query =
        petOwners
        .SelectMany(petOwner => petOwner.Pets, (petOwner, petName) => new { petOwner, petName })
        .Where(ownerAndPet => ownerAndPet.petName.StartsWith("S"))
        .Select(ownerAndPet =>
                new
                {
                    Owner = ownerAndPet.petOwner.Name,
                    Pet = ownerAndPet.petName
                }
        );

    // Print the results.
    foreach (var obj in query)
    {
        Console.WriteLine(obj);
    }
}

// This code produces the following output:
//
// {Owner=Higa, Pet=Scruffy}
// {Owner=Higa, Pet=Sam}
// {Owner=Ashkenazi, Pet=Sugar}
// {Owner=Price, Pet=Scratches}
Structure PetOwner
    Public Name As String
    Public Pets() As String
End Structure

Sub SelectManyEx3()
    ' Create an array of PetOwner objects.
    Dim petOwners() As PetOwner =
{New PetOwner With
 {.Name = "Higa", .Pets = New String() {"Scruffy", "Sam"}},
 New PetOwner With
 {.Name = "Ashkenazi", .Pets = New String() {"Walker", "Sugar"}},
 New PetOwner With
 {.Name = "Price", .Pets = New String() {"Scratches", "Diesel"}},
 New PetOwner With
 {.Name = "Hines", .Pets = New String() {"Dusty"}}}

    ' Project an anonymous type that consists of
    ' the owner's name and the pet's name (string).
    Dim query =
petOwners _
.SelectMany(
    Function(petOwner) petOwner.Pets,
    Function(petOwner, petName) New With {petOwner, petName}) _
.Where(Function(ownerAndPet) ownerAndPet.petName.StartsWith("S")) _
.Select(Function(ownerAndPet) _
       New With {.Owner = ownerAndPet.petOwner.Name,
                 .Pet = ownerAndPet.petName
       })

    Dim output As New System.Text.StringBuilder
    For Each obj In query
        output.AppendLine(String.Format("Owner={0}, Pet={1}", obj.Owner, obj.Pet))
    Next

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

' This code produces the following output:
'
' Owner=Higa, Pet=Scruffy
' Owner=Higa, Pet=Sam
' Owner=Ashkenazi, Pet=Sugar
' Owner=Price, Pet=Scratches

備註

實作這個方法是使用延後的執行。This method is implemented by using deferred execution. 立即傳回值是儲存,才能執行此動作的所有資訊的物件。The immediate return value is an object that stores all the information that is required to perform the action. 這個方法所表示的查詢不會執行直到列舉物件可以藉由呼叫其GetEnumerator方法直接或透過foreachVisual C# 中或For EachVisual Basic 中。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.

SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>)方法會很有用,當您要保留的項目source在呼叫之後,就會發生的查詢邏輯的範圍內SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>)The SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>) method is useful when you have to keep the elements of source in scope for query logic that occurs after the call to SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>). 如需程式碼範例,請參閱<範例>一節。See the Example section for a code example. 如果類型的物件之間沒有雙向關聯性TSource和類型的物件TCollection,也就是如果型別的物件TCollection提供屬性,以擷取TSource物件產生,您並不需要此多載SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>)If there is a bidirectional relationship between objects of type TSource and objects of type TCollection, that is, if an object of type TCollection provides a property to retrieve the TSource object that produced it, you do not need this overload of SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>). 相反地,您可以使用SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TResult>>)並瀏覽回到TSource物件傳遞TCollection物件。Instead, you can use SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TResult>>) and navigate back to the TSource object through the TCollection object.

在查詢運算式語法中,每個from子句 (Visual C#) 或From初始子句 (Visual Basic) 其中一個將轉譯的引動過程SelectManyIn query expression syntax, each from clause (Visual C#) or From clause (Visual Basic) after the initial one translates to an invocation of SelectMany.

另請參閱

SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>) SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>) SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>) SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>)

每個序列的項目至IEnumerable<T>壓平合併成單一序列,產生的序列,其中叫用結果選取器函式,每個項目。Projects each element of a sequence to an IEnumerable<T>, flattens the resulting sequences into one sequence, and invokes a result selector function on each element therein. 各來源項目的索引是在該項目的中繼投影表單中使用。The index of each source element is used in the intermediate projected form of that element.

public:
generic <typename TSource, typename TCollection, typename TResult>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::IEnumerable<TResult> ^ SelectMany(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, int, System::Collections::Generic::IEnumerable<TCollection> ^> ^ collectionSelector, Func<TSource, TCollection, TResult> ^ resultSelector);
public static System.Collections.Generic.IEnumerable<TResult> SelectMany<TSource,TCollection,TResult> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,int,System.Collections.Generic.IEnumerable<TCollection>> collectionSelector, Func<TSource,TCollection,TResult> resultSelector);
static member SelectMany : seq<'Source> * Func<'Source, int, seq<'Collection>> * Func<'Source, 'Collection, 'Result> -> seq<'Result>
<Extension()>
Public Function SelectMany(Of TSource, TCollection, TResult) (source As IEnumerable(Of TSource), collectionSelector As Func(Of TSource, Integer, IEnumerable(Of TCollection)), resultSelector As Func(Of TSource, TCollection, TResult)) As IEnumerable(Of TResult)

類型參數

TSource

source 項目的類型。The type of the elements of source.

TCollection

所收集之中繼項目的型別collectionSelectorThe type of the intermediate elements collected by collectionSelector.

TResult

產生的序列的項目類型。The type of the elements of the resulting sequence.

參數

source
IEnumerable<TSource>

要投影的值序列。A sequence of values to project.

collectionSelector
Func<TSource,Int32,IEnumerable<TCollection>>

要套用到每個來源項目的轉換函式;此函式的第二個參數代表來源項目的索引。A transform function to apply to each source element; the second parameter of the function represents the index of the source element.

resultSelector
Func<TSource,TCollection,TResult>

若要套用到中繼序列各個項目的轉換函式。A transform function to apply to each element of the intermediate sequence.

傳回

IEnumerable<TResult>

IEnumerable<T>其項目是叫用來從一對多轉換函式的結果collectionSelector各項目上source然後再將每個序列項目及其對應的來源項目對應至結果項目。An IEnumerable<T> whose elements are the result of invoking the one-to-many transform function collectionSelector on each element of source and then mapping each of those sequence elements and their corresponding source element to a result element.

例外狀況

sourcecollectionSelectorresultSelectornullsource or collectionSelector or resultSelector is null.

備註

實作這個方法是使用延後的執行。This method is implemented by using deferred execution. 立即傳回值是儲存,才能執行此動作的所有資訊的物件。The immediate return value is an object that stores all the information that is required to perform the action. 這個方法所表示的查詢不會執行直到列舉物件可以藉由呼叫其GetEnumerator方法直接或透過foreachVisual C# 中或For EachVisual Basic 中。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.

SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>)方法會很有用,當您要保留的項目source在呼叫之後,就會發生的查詢邏輯的範圍內SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>)The SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>) method is useful when you have to keep the elements of source in scope for query logic that occurs after the call to SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>). 如需程式碼範例,請參閱<範例>一節。See the Example section for a code example. 如果類型的物件之間沒有雙向關聯性TSource和類型的物件TCollection,也就是如果型別的物件TCollection提供屬性,以擷取TSource物件產生,您並不需要此多載SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>)If there is a bidirectional relationship between objects of type TSource and objects of type TCollection, that is, if an object of type TCollection provides a property to retrieve the TSource object that produced it, you do not need this overload of SelectMany<TSource,TCollection,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TCollection>>, Func<TSource,TCollection,TResult>). 相反地,您可以使用SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TResult>>)並瀏覽回到TSource物件傳遞TCollection物件。Instead, you can use SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TResult>>) and navigate back to the TSource object through the TCollection object.

SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TResult>>) SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TResult>>) SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TResult>>) SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TResult>>)

每個序列的項目至IEnumerable<T>和壓平合併成單一序列產生的序列。Projects each element of a sequence to an IEnumerable<T> and flattens the resulting sequences into one sequence.

public:
generic <typename TSource, typename TResult>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::IEnumerable<TResult> ^ SelectMany(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, System::Collections::Generic::IEnumerable<TResult> ^> ^ selector);
public static System.Collections.Generic.IEnumerable<TResult> SelectMany<TSource,TResult> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,System.Collections.Generic.IEnumerable<TResult>> selector);
static member SelectMany : seq<'Source> * Func<'Source, seq<'Result>> -> seq<'Result>
<Extension()>
Public Function SelectMany(Of TSource, TResult) (source As IEnumerable(Of TSource), selector As Func(Of TSource, IEnumerable(Of TResult))) As IEnumerable(Of TResult)

類型參數

TSource

source 項目的類型。The type of the elements of source.

TResult

所傳回的序列的項目類型selectorThe type of the elements of the sequence returned by selector.

參數

source
IEnumerable<TSource>

要投影的值序列。A sequence of values to project.

selector
Func<TSource,IEnumerable<TResult>>

要套用至每個項目的轉換函式。A transform function to apply to each element.

傳回

IEnumerable<TResult>

IEnumerable<T>其項目是叫用的輸入序列的每個項目-一對多轉換函式的結果。An IEnumerable<T> whose elements are the result of invoking the one-to-many transform function on each element of the input sequence.

例外狀況

sourceselectornullsource or selector is null.

範例

下列程式碼範例示範如何使用SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TResult>>)對陣列進行反覆執行的一對多投影。The following code example demonstrates how to use SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TResult>>) to perform a one-to-many projection over an array.

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
*/
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

備註

實作這個方法是使用延後的執行。This method is implemented by using deferred execution. 立即傳回值是儲存,才能執行此動作的所有資訊的物件。The immediate return value is an object that stores all the information that is required to perform the action. 這個方法所表示的查詢不會執行直到列舉物件可以藉由呼叫其GetEnumerator方法直接或透過foreachVisual C# 中或For EachVisual Basic 中。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.

SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TResult>>)方法列舉輸入的序列中,使用轉換函式對應至每個項目IEnumerable<T>,然後列舉,並產生每個這類的項目IEnumerable<T>物件。The SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TResult>>) method enumerates the input sequence, uses a transform function to map each element to an IEnumerable<T>, and then enumerates and yields the elements of each such IEnumerable<T> object. 也就是說,每個項目sourceselector叫用,而且會傳回一連串的值。That is, for each element of source, selector is invoked and a sequence of values is returned. SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TResult>>) 然後將壓平合併成一維集合的這個二維集合IEnumerable<T>並將它傳回。SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TResult>>) then flattens this two-dimensional collection of collections into a one-dimensional IEnumerable<T> and returns it. 比方說,如果查詢使用SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TResult>>)取得訂單 (型別的Order) 資料庫中每位客戶,則結果為類型IEnumerable<Order>在 C# 或IEnumerable(Of Order)Visual Basic 中。For example, if a query uses SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,IEnumerable<TResult>>) 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. 如果改為查詢使用Select若要取得的訂單,未合併的訂單集合的集合,且結果為型別的IEnumerable<List<Order>>在 C# 或IEnumerable(Of List(Of Order))Visual Basic 中。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.

在查詢運算式語法中,每個from子句 (Visual C#) 或From初始子句 (Visual Basic) 其中一個將轉譯的引動過程SelectManyIn query expression syntax, each from clause (Visual C#) or From clause (Visual Basic) after the initial one translates to an invocation of SelectMany.

另請參閱

SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TResult>>) SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TResult>>) SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TResult>>) SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TResult>>)

每個序列的項目至IEnumerable<T>,並將簡化成單一序列產生的序列。Projects each element of a sequence to an IEnumerable<T>, and flattens the resulting sequences into one sequence. 各來源項目的索引是在該項目的投影表單中使用。The index of each source element is used in the projected form of that element.

public:
generic <typename TSource, typename TResult>
[System::Runtime::CompilerServices::Extension]
 static System::Collections::Generic::IEnumerable<TResult> ^ SelectMany(System::Collections::Generic::IEnumerable<TSource> ^ source, Func<TSource, int, System::Collections::Generic::IEnumerable<TResult> ^> ^ selector);
public static System.Collections.Generic.IEnumerable<TResult> SelectMany<TSource,TResult> (this System.Collections.Generic.IEnumerable<TSource> source, Func<TSource,int,System.Collections.Generic.IEnumerable<TResult>> selector);
static member SelectMany : seq<'Source> * Func<'Source, int, seq<'Result>> -> seq<'Result>
<Extension()>
Public Function SelectMany(Of TSource, TResult) (source As IEnumerable(Of TSource), selector As Func(Of TSource, Integer, IEnumerable(Of TResult))) As IEnumerable(Of TResult)

類型參數

TSource

source 項目的類型。The type of the elements of source.

TResult

所傳回的序列的項目類型selectorThe type of the elements of the sequence returned by selector.

參數

source
IEnumerable<TSource>

要投影的值序列。A sequence of values to project.

selector
Func<TSource,Int32,IEnumerable<TResult>>

要套用到每個來源項目的轉換函式;此函式的第二個參數代表來源項目的索引。A transform function to apply to each source element; the second parameter of the function represents the index of the source element.

傳回

IEnumerable<TResult>

IEnumerable<T>其項目是叫用的輸入序列的每個項目-一對多轉換函式的結果。An IEnumerable<T> whose elements are the result of invoking the one-to-many transform function on each element of an input sequence.

例外狀況

sourceselectornullsource or selector is null.

範例

下列程式碼範例示範如何使用SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TResult>>)對陣列進行反覆執行的一對多投影,並使用每個外部項目的索引。The following code example demonstrates how to use SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TResult>>) to perform a one-to-many projection over an array and use the index of each outer element.

class PetOwner
{
    public string Name { get; set; }
    public List<string> Pets { get; set; }
}

public static void SelectManyEx2()
{
    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" } },
          new PetOwner { Name="Hines, Patrick", 
              Pets = new List<string>{ "Dusty" } } };

    // Project the items in the array by appending the index 
    // of each PetOwner to each pet's name in that petOwner's 
    // array of pets.
    IEnumerable<string> query =
        petOwners.SelectMany((petOwner, index) =>
                                 petOwner.Pets.Select(pet => index + pet));

    foreach (string pet in query)
    {
        Console.WriteLine(pet);
    }
}

// This code produces the following output:
//
// 0Scruffy
// 0Sam
// 1Walker
// 1Sugar
// 2Scratches
// 2Diesel
// 3Dusty
Structure PetOwner
    Public Name As String
    Public Pets() As String
End Structure

Sub SelectManyEx2()
    ' 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"}},
 New PetOwner With
 {.Name = "Hines, Patrick", .Pets = New String() {"Dusty"}}}

    ' Project the items in the array by appending the index 
    ' of each PetOwner to each pet's name in that petOwner's 
    ' array of pets.
    Dim query As IEnumerable(Of String) =
petOwners.SelectMany(Function(petOwner, index) _
                         petOwner.Pets.Select(Function(pet) _
                                                  index.ToString() + pet))

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

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

備註

實作這個方法是使用延後的執行。This method is implemented by using deferred execution. 立即傳回值是儲存,才能執行此動作的所有資訊的物件。The immediate return value is an object that stores all the information that is required to perform the action. 這個方法所表示的查詢不會執行直到列舉物件可以藉由呼叫其GetEnumerator方法直接或透過foreachVisual C# 中或For EachVisual Basic 中。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.

SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TResult>>)方法列舉輸入的序列中,使用轉換函式對應至每個項目IEnumerable<T>,然後列舉,並產生每個這類的項目IEnumerable<T>物件。The SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TResult>>) method enumerates the input sequence, uses a transform function to map each element to an IEnumerable<T>, and then enumerates and yields the elements of each such IEnumerable<T> object. 也就是說,每個項目sourceselector叫用,而且會傳回一連串的值。That is, for each element of source, selector is invoked and a sequence of values is returned. SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TResult>>) 然後將壓平合併成一維集合的這個二維集合IEnumerable<T>並將它傳回。SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TResult>>) then flattens this two-dimensional collection of collections into a one-dimensional IEnumerable<T> and returns it. 比方說,如果查詢使用SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TResult>>)取得訂單 (型別的Order) 資料庫中每位客戶,則結果為類型IEnumerable<Order>在 C# 或IEnumerable(Of Order)Visual Basic 中。For example, if a query uses SelectMany<TSource,TResult>(IEnumerable<TSource>, Func<TSource,Int32,IEnumerable<TResult>>) 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. 如果改為查詢使用Select若要取得的訂單,未合併的訂單集合的集合,且結果為型別的IEnumerable<List<Order>>在 C# 或IEnumerable(Of List(Of Order))Visual Basic 中。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.

第一個引數selector代表要處理的項目。The first argument to selector represents the element to process. 第二個引數selector代表來源序列中的該項目的以零為起始的索引。The second argument to selector represents the zero-based index of that element in the source sequence. 如果項目是已知的順序,而且您想要運用特定的索引處的項目,例如,這可以是很有用。This can be useful if the elements are in a known order and you want to do something with an element at a particular index, for example. 它也可用如果您想要擷取的一或多個項目索引。It can also be useful if you want to retrieve the index of one or more elements.

適用於