title: How do you use max_by with an enumerable if you need to filter out values?
body: <p>How would I do this?  Right now it's creating nil values when user is male, and then the &lt;==> operation is failing.  </p>
  
  <pre><code>@user.max_by{|user_id, user| user.height if user.female?}
  </code></pre>