title: Merging two IEnumerable<T>s
body: <p>I have two <code>IEnumerable&lt;T&gt;</code>s.</p>
  
  <p>One gets filled with the fallback ellements. This one will always contain the most elements.
  The other one will get filled depending on some parameters and will possibly contain less elements.
  If an element doesn't exist in the second one, I need to fill it with the equivalent one of the first one.</p>
  
  <p>This code does the job, but feels inefficient to me and requires me to cast the IEnumerables to ILists or to use a temporary list
  Person implements IEquatable</p>
  
  <pre><code>IEnumerable&lt;Person&gt; fallBack = Repository.GetPersons();
  IList&lt;Person&gt; translated = Repository.GetPersons(language).ToList();
  
  foreach (Person person in fallBack)
  {
      if (!translated.Any(p=&gt;p.equals(person)))
          translated.add(person);  
  }
  </code></pre>
  
  <p>Any suggestions?</p>