title: Custom Sorting a vector of tuples
body: <p>I have a vector of tuples like </p>
  
  <pre><code>vector&lt;tuple&lt;T1, T2, T3&gt;&gt; v;
  </code></pre>
  
  <p>I believe that when the default comparison kicks in for tuple types, it performs a lexicographical comparison. </p>
  
  <p>Can I perform the comparisons by the element I choose ? Eg by the second element in the above example or by the ith element in a tuple containing m types ? </p>
  
  <p>Thank you in advance. </p>