title: Convert list encasing inside data frame row values
body: <p>I have a Pandas Series that has list elements in each row.
  I want to de-list those values and store them back in the series.
  It looks like this. Can someone please help?</p>
  
  <pre><code>0                           ['Harvard business review']
  1                           ['Harvard business review']
  2     ['Journal of Medical Marketing: Device, Diagno...
  3                           ['Harvard business review']
  4                    ['Science Translational Medicine']
  5                    ['Science Translational Medicine']
  6                                       ['Tetrahedron']
  7                                       ['Tetrahedron']
  8                                           ['bioRxiv']
  9                                           ['Science']
  10                                     ['Cell Systems']
  11                                       ['Prescriber']
  12                                             ['Cell']
  </code></pre>
  
  <p>I tried to convert each into a list and then extract the values, but it would not convert to list.</p>