title: How to know the number of elements in a column that are stored as an array in Pandas dataframe
body: <p>I have a result of a dataframe that looks like this:</p>
  
  <pre><code>Factor      OccurIn
  Accelerator [41, 81, 62]
  Breaks      [51, 11, 12, 13]
  Vision      [58, 31, 92, 67, 68]
  </code></pre>
  
  <p>How can I copy that frame into a new one having a column summing the number of elements that are in an array like:</p>
  
  <pre><code>Factor      n
  Accelerator 3
  Breaks      4
  Vision      5
  </code></pre>