title: Merge a List of pojos into a Map of integers that can be combined on a key
body: <p>I am trying to stream-ify the following logic: </p>
  
  <p>I have a map of Integer ids to an integer count. I have a list of Pojos that represent the ids. I want to merge the two and have a map of pojos to integer count. </p>
  
  <p>Currently I have:</p>
  
  <pre><code>  return EntryStream.of(idToCountMapping)
        .mapKeys(k -&gt; StreamEx.of(pojos).findFirst(s -&gt; s.getId().equals(k)))
        .filterKeys(Optional::isPresent)
        .mapKeys(Optional::get)
        .mapKeyValue(SuperCoolNewPojo::new)
        .toList(); 
  </code></pre>
  
  <p>The first <code>mapKeys()</code> call strikes me as something that is probably much better expressed in a different way. </p>
  
  <p>Any help would be great!</p>
  
  <p>Thanks, 
  Anthony</p>