title: pandas get unique values from column of lists
body: <p>How do I get the unique values of a column of lists in pandas or numpy such that second column from</p>
  <p><a href="https://i.stack.imgur.com/k971P.png" rel="noreferrer"><img src="https://i.stack.imgur.com/k971P.png" alt="enter image description here" /></a></p>
  <p>would result in <code>'action', 'crime', 'drama'</code>.</p>
  <p>The closest (but non-functional) solutions I could come up with were:</p>
  <pre><code> genres = data['Genre'].unique()
  </code></pre>
  <p>But this predictably results in a TypeError saying how lists aren't hashable.</p>
  <p><code>TypeError: unhashable type: 'list'</code></p>
  <p>Set seemed to be a good idea but</p>
  <p><code> genres = data.apply(set(), columns=['Genre'], axis=1)</code></p>
  <p>but also results in a
  <code>TypeError: set() takes no keyword arguments</code></p>