title: pandas - how to work with arrays in cells
body: <p>I have a dataframe with arrays. Example:</p>
  
  <pre><code>df = pd.DataFrame([('a', [1,2,3]), ('b', [4,5,6])], columns=['name', 'values'])
  
    name     values
  0    a  [1, 2, 3]
  1    b  [4, 5, 6]
  </code></pre>
  
  <p>I know that the <code>values</code> col arrays are of the same length.
  I want to calculate the average on axis=0 of the values arrays.
  In numpy I could do it like:</p>
  
  <pre><code>np.array([[1,2,3], [4,5,6]]).mean(axis=0) # result: array([2.5, 3.5, 4.5])
  </code></pre>
  
  <p>Is it possible with plain pandas?<br>
  If not, how can I easily convert the values col to a numpy array?
  I've tried <code>df['values'].values</code>, but this does not gives a matrix:</p>
  
  <pre><code>array([list([1, 2, 3]), list([4, 5, 6])], dtype=object)
  </code></pre>