title: Converting a pandas series to a string array
body: <p>I have a pandas dataframe:</p>
  
  <pre><code>ind  
  0   ['C']
  1   ['C']
  2   ['C']
  3   ['C']
  4   ['E']
  5   ['E']
  </code></pre>
  
  <p>I want to convert it into a string: <code>CCCCEE</code></p>