title: Pandas dataframe split array entry into two columns
body: <p>I have a data frame that looks like this:</p>
  
  <pre><code>       reviewerID        asin    reviewerName helpful  unixReviewTime  \
  0  A1N4O8VOJZTDVB  B004A9SDD8  Annette Yancey  [1, 1]      1383350400   
  </code></pre>
  
  <p>I'd like to split the 'helpful' column into two different columns with names 'helpful_numerator' and 'helpful denominator and I can't figure it out.</p>
  
  <p>Any help would be much appreciated!</p>