title: How to order set<pair<unsigned int, double> > by the second value of pair?
body: <p>As the title says, I've built a <code>set</code> of <code>pair</code> of values that I need ordered by the <code>double value</code> (second): </p>
  
  <p><code>set&lt;pair&lt;unsigned int, double&gt; &gt; s</code></p>