title: Order each element of each group within an ObservableCollection<>
body: <p>I have a <code>ObservableCollection&lt;&gt;</code> with some groups in it.</p>
  <p>Each group has some elements.
  I wish I could reverse every element within the group, in descending <code>DateTime</code> order, while currently they are in ascending order.</p>
  <p>I tried with this code, but the orders of the groups are simply reversed, not the elements within it:</p>
  <p>UPDATE:</p>
  <pre><code>  public class Group : ObservableCollection&lt;Diary&gt;
          {
                  public string Name { get; private set; }
      
                  public Group(string name, ObservableCollection&lt;Diary&gt; icon) : base(icon)
                  {
                      Name = name;                    
                  }
           }
  
  public ObservableCollection&lt;Group&gt; Obj { get; private set; } = new ObservableCollection&lt;Group&gt;();
          ....
  Group group = new Group(&quot;&quot;, new ObservableCollection&lt;Group&gt;());
   
  </code></pre>
  <p>UPDATE:</p>
  <pre><code>Obj.Add(group);
  group.Add(element);
  group.Add(element2);
  group.Reverse()
      
  </code></pre>