Enumerable.GroupJoin<TOuter, TInner, TKey, TResult> Method (IEnumerable<TOuter>, IEnumerable<TInner>, Func<TOuter, TKey>, Func<TInner, TKey>, Func<TOuter, IEnumerable<TInner>, TResult>)

Type Parameters

• TOuter
  The type of the elements of the first sequence.

• TInner
  The type of the elements of the second sequence.

• TKey
  The type of the keys returned by the key selector functions.

• TResult
  The type of the result elements.

Parameters

• outer
  Type: System.Collections.Generic.IEnumerable<TOuter>
  The first sequence to join.

• inner
  Type: System.Collections.Generic.IEnumerable<TInner>
  The sequence to join to the first sequence.

• outerKeySelector
  Type: System.Func<TOuter, TKey>
  A function to extract the join key from each element of the first sequence.

• innerKeySelector
  Type: System.Func<TInner, TKey>
  A function to extract the join key from each element of the second sequence.

• resultSelector
  Type: System.Func<TOuter, IEnumerable<TInner>, TResult>
  A function to create a result element from an element from the first sequence and a collection of matching elements from the second sequence.

Return Value

Type: System.Collections.Generic.IEnumerable<TResult>
An IEnumerable<T> that contains elements of type TResult that are obtained by performing a grouped join on two sequences.

   Structure Person
      Public Name As String
   End Structure

   Structure Pet
      Public Name As String
      Public Owner As Person
   End Structure

   Sub GroupJoinEx1()
      Dim magnus As New Person With {.Name = "Hedlund, Magnus"}
      Dim terry As New Person With {.Name = "Adams, Terry"}
      Dim charlotte As New Person With {.Name = "Weiss, Charlotte"}

      Dim barley As New Pet With {.Name = "Barley", .Owner = terry}
      Dim boots As New Pet With {.Name = "Boots", .Owner = terry}
      Dim whiskers As New Pet With {.Name = "Whiskers", .Owner = charlotte}
      Dim daisy As New Pet With {.Name = "Daisy", .Owner = magnus}

      Dim people As New List(Of Person)(New Person() {magnus, terry, charlotte})
      Dim pets As New List(Of Pet)(New Pet() {barley, boots, whiskers, daisy})

      ' Create a collection where each element is an anonymous type
      ' that contains a Person's name and a collection of names of 
      ' the pets that are owned by them.
      Dim query = _
          people.GroupJoin(pets, _
                     Function(person) person, _
                     Function(pet) pet.Owner, _
                     Function(person, petCollection) _
                         New With {.OwnerName = person.Name, _
                                   .Pets = petCollection.Select( _
                                                      Function(pet) pet.Name)})

      Dim output As New System.Text.StringBuilder
      For Each obj In query
         ' Output the owner's name.
         output.AppendLine(obj.OwnerName & ":")
         ' Output each of the owner's pet's names.
         For Each pet As String In obj.Pets
            output.AppendLine("  " & pet)
         Next
      Next

      ' Display the output.
      outputBlock.Text &= output.ToString() & vbCrLf
   End Sub

   ' This code produces the following output:
   '
   ' Hedlund, Magnus
   '   Daisy
   ' Adams, Terry
   '   Barley
   '   Boots
   ' Weiss, Charlotte
   '   Whiskers

      class Person
      {
         public string Name { get; set; }
      }

      class Pet
      {
         public string Name { get; set; }
         public Person Owner { get; set; }
      }

      public static void GroupJoinEx1()
      {
         Person magnus = new Person { Name = "Hedlund, Magnus" };
         Person terry = new Person { Name = "Adams, Terry" };
         Person charlotte = new Person { Name = "Weiss, Charlotte" };

         Pet barley = new Pet { Name = "Barley", Owner = terry };
         Pet boots = new Pet { Name = "Boots", Owner = terry };
         Pet whiskers = new Pet { Name = "Whiskers", Owner = charlotte };
         Pet daisy = new Pet { Name = "Daisy", Owner = magnus };

         List<Person> people = new List<Person> { magnus, terry, charlotte };
         List<Pet> pets = new List<Pet> { barley, boots, whiskers, daisy };

         // Create a list where each element is an anonymous 
         // type that contains a person's name and 
         // a collection of names of the pets they own.
         var query =
             people.GroupJoin(pets,
                              person => person,
                              pet => pet.Owner,
                              (person, petCollection) =>
                                  new
                                  {
                                     OwnerName = person.Name,
                                     Pets = petCollection.Select(pet => pet.Name)
                                  });

         foreach (var obj in query)
         {
            // Output the owner's name.
            outputBlock.Text += String.Format("{0}:", obj.OwnerName) + "\n";
            // Output each of the owner's pet's names.
            foreach (string pet in obj.Pets)
            {
               outputBlock.Text += String.Format("  {0}", pet) + "\n";
            }
         }
      }

      /*
       This code produces the following output:

       Hedlund, Magnus:
         Daisy
       Adams, Terry:
         Barley
         Boots
       Weiss, Charlotte:
         Whiskers
      */