title: Sort by two fields, with the second being reverse alphabetical one-liner
body: <p>I want to sort a collection such as:</p>
  <pre><code>[['hello', 'world', 'my'], ['name', 'is', 'foo'], ['bar']]
  </code></pre>
  <p>First by size of each element, then by <strong>reverse</strong> alphabetical order of the first element in each element in a one-liner so the result would be</p>
  <pre><code>[['bar'],['name','is','foo'],['hello','world','my']]
  </code></pre>
  <p>I have tried
  <code>groups.sort_by { |group| [group.length, -group.first] }</code> but the '-' doesn't work here. Any ideas?</p>