Enumerable.ThenByDescending<TSource, TKey> Method (IOrderedEnumerable<TSource>, Func<TSource, TKey>, IComparer<TKey>)

Type Parameters

• TSource
  The type of the elements of source.

• TKey
  The type of the key returned by keySelector.

Parameters

• source
  Type: System.Linq.IOrderedEnumerable<TSource>
  An IOrderedEnumerable<TElement> that contains elements to sort.

• keySelector
  Type: System.Func<TSource, TKey>
  A function to extract a key from each element.

• comparer
  Type: System.Collections.Generic.IComparer<TKey>
  An IComparer<T> to compare keys.

Return Value

Type: System.Linq.IOrderedEnumerable<TSource>
An IOrderedEnumerable<TElement> whose elements are sorted in descending order according to a key.

   ' This class provides a custom implementation of the Compare() method.
   Class CaseInsensitiveComparer
      Implements IComparer(Of String)

      Function Compare(ByVal x As String, ByVal y As String) As Integer _
          Implements IComparer(Of String).Compare

         ' Compare values and ignore case.
         Return String.Compare(x, y, True)
      End Function
   End Class

   Sub ThenByDescendingEx1()
      Dim fruits() As String = _
          {"apPLe", "baNanA", "apple", "APple", "orange", "BAnana", "ORANGE", "apPLE"}

      ' Sort the strings first by their length and then 
      ' by using a custom "case insensitive" comparer.
      Dim query As IEnumerable(Of String) = _
          fruits _
          .OrderBy(Function(fruit) fruit.Length) _
          .ThenByDescending(Function(fruit) fruit, New CaseInsensitiveComparer())

      ' Display the results.
      Dim output As New System.Text.StringBuilder
      For Each fruit As String In query
         output.AppendLine(fruit)
      Next
      outputBlock.Text &= output.ToString() & vbCrLf
   End Sub

   ' This code produces the following output:

   ' apPLe
   ' apple
   ' APple
   ' apPLE
   ' orange
   ' ORANGE
   ' baNanA
   ' BAnana

      public class CaseInsensitiveComparer : IComparer<string>
      {
         public int Compare(string x, string y)
         {
            return string.Compare(x, y, StringComparison.CurrentCultureIgnoreCase);
         }
      }

      public static void ThenByDescendingEx1()
      {
         string[] fruits = { "apPLe", "baNanA", "apple", "APple", "orange", "BAnana", "ORANGE", "apPLE" };

         // Sort the strings first ascending by their length and 
         // then descending using a custom case insensitive comparer.
         IEnumerable<string> query =
             fruits
             .OrderBy(fruit => fruit.Length)
             .ThenByDescending(fruit => fruit, new CaseInsensitiveComparer());

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

      /*
          This code produces the following output:

          apPLe
          apple
          APple
          apPLE
          orange
          ORANGE
          baNanA
          BAnana
      */