Enumerable.SelectMany<TSource, TResult> Method (IEnumerable<TSource>, Func<TSource, IEnumerable<TResult>>)

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.Generic.IEnumerable<TSource>
  A sequence of values to project.

• selector
  Type: System.Func<TSource, IEnumerable<TResult>>
  A transform function to apply to each element.

Return Value

Type: System.Collections.Generic.IEnumerable<TResult>
An IEnumerable<T> whose elements are the result of invoking the one-to-many transform function on each element of the input sequence.

   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.
      outputBlock.Text &= output.ToString() & vbCrLf
   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);

         outputBlock.Text += "Using SelectMany():" + "\n";

         // Only one foreach loop is required to iterate 
         // through the results since it is a
         // one-dimensional collection.
         foreach (string pet in query1)
         {
            outputBlock.Text += pet + "\n";
         }

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

         outputBlock.Text += "\nUsing Select():" + "\n";

         // 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)
            {
               outputBlock.Text += pet + "\n";
            }
            outputBlock.Text += "\n";
         }
      }

      /*
       This code produces the following output:

       Using SelectMany():
       Scruffy
       Sam
       Walker
       Sugar
       Scratches
       Diesel

       Using Select():
       Scruffy
       Sam

       Walker
       Sugar

       Scratches
       Diesel
      */