title: Split a list of tuples into sub-lists of the same tuple field
body: <p>I have a huge list of tuples in this format. The second field of the each tuple is the category field.</p>
  
  <pre><code>    [(1, 'A', 'foo'),
      (2, 'A', 'bar'),
      (100, 'A', 'foo-bar'),
  
      ('xx', 'B', 'foobar'),
      ('yy', 'B', 'foo'),
  
      (1000, 'C', 'py'),
      (200, 'C', 'foo'),
      ..]
  </code></pre>
  
  <p>What is the most efficient way to break it down into sub-lists of the same category ( A, B, C .,etc)?</p>