title: pandas: convert multiple categories to dummies
body: <p>I have a table where each row can belong to multiple categories such as,</p>
  
  <pre><code>test = pd.DataFrame({
              'name': ['a', 'b'],
              'category': [['cat1', 'cat2'],['cat1', 'cat3']]
      })
  </code></pre>
  
  <p>How can I convert each category to a dummy variable in such a way that the above table becomes,</p>
  
  <pre><code>test_res = pd.DataFrame({
          'name': ['a', 'b'],
          'cat1': [1, 1],
          'cat2': [1, 0],
          'cat3': [0, 1]
      })
  </code></pre>
  
  <p>I tried <code>pd.get_dummies(test['category'])</code> but get the following error,</p>
  
  <pre><code>TypeError: unhashable type: 'list'
  </code></pre>