Enumerable.Empty<TResult> Method

Type Parameters

• TResult
  The type to assign to the type parameter of the returned generic IEnumerable<T>.

Return Value

Type: System.Collections.Generic.IEnumerable<TResult>
An empty IEnumerable<T> whose type argument is TResult.

' Create an empty sequence.
Dim empty As IEnumerable(Of Decimal) = Enumerable.Empty(Of Decimal)()

IEnumerable<decimal> empty = Enumerable.Empty<decimal>();

      ' Create three string arrays.
      Dim names1() As String = _
          {"Hartono, Tommy"}
      Dim names2() As String = _
          {"Adams, Terry", "Andersen, Henriette Thaulow", "Hedlund, Magnus", "Ito, Shu"}
      Dim names3() As String = _
          {"Solanki, Ajay", "Hoeing, Helge", "Andersen, Henriette Thaulow", "Potra, Cristina", "Iallo, Lucio"}

      ' Create a List that contains 3 elements, where
      ' each element is an array of strings.
      Dim namesList As New List(Of String())(New String()() {names1, names2, names3})

      ' Select arrays that have four or more elements and union
      ' them into one collection, using Empty() to generate the 
      ' empty collection for the seed value.
      Dim allNames As IEnumerable(Of String) = _
          namesList.Aggregate(Enumerable.Empty(Of String)(), _
                              Function(current, nextOne) _
                                  IIf(nextOne.Length > 3, current.Union(nextOne), current))

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

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

      ' This code produces the following output:
      '
      ' Adams, Terry
      ' Andersen, Henriette Thaulow
      ' Hedlund, Magnus
      ' Ito, Shu
      ' Solanki, Ajay
      ' Hoeing, Helge
      ' Potra, Cristina
      ' Iallo, Lucio

      string[] names1 = { "Hartono, Tommy" };
      string[] names2 = { "Adams, Terry", "Andersen, Henriette Thaulow",
                               "Hedlund, Magnus", "Ito, Shu" };
      string[] names3 = { "Solanki, Ajay", "Hoeing, Helge",
                               "Andersen, Henriette Thaulow",
                               "Potra, Cristina", "Iallo, Lucio" };

      List<string[]> namesList =
          new List<string[]> { names1, names2, names3 };

      // Only include arrays that have four or more elements
      IEnumerable<string> allNames =
          namesList.Aggregate(Enumerable.Empty<string>(),
          (current, next) => next.Length > 3 ? current.Union(next) : current);

      foreach (string name in allNames)
      {
         outputBlock.Text += name + "\n";
      }

      /*
       This code produces the following output:

       Adams, Terry
       Andersen, Henriette Thaulow
       Hedlund, Magnus
       Ito, Shu
       Solanki, Ajay
       Hoeing, Helge
       Potra, Cristina
       Iallo, Lucio
      */