title: Python: Extract list from inside the list and remove duplicates
body: <p>I have a dataframe with a column that consists of lists of lists (of varying length).
  One example:
  <code>df['east'][0]</code> gives</p>
  
  <pre><code>[array(['Indonesia', 'New Zealand'], dtype=object), array(['Indonesia', 'New Zealand'], dtype=object)]
  </code></pre>
  
  <p>I want to merge the lists inside of this bigger list and get rid of duplicates and make sure that data is presented clearly, i.e. simply</p>
  
  <pre><code>['Indonesia', 'New Zealand']
  </code></pre>
  
  <p>I tried <a href="https://stackoverflow.com/questions/30565759/get-unique-values-in-list-of-lists-in-python">some suggestions from here</a> to remove duplicates, but, for example,for <code>np.unique(functools.reduce(operator.add, east))</code> Python said "ValueError: operands could not be broadcast together with shapes (4,) (13,)"</p>
  
  <p>I could usually solve problems, but here I am not sure what is happening - what are these arrays in the list.</p>