title: Average of a Series in a DataFrame
body: <p>I have a dataframe that looks something like this:</p>
  
  <pre><code>values
  [0.0,12.34,223.12,4.55,...]
  [0.0,78.12,12.90,...]
  .
  .
  . 
  </code></pre>
  
  <p>I am trying to calculate the average of the value column and store that number in a new column.</p>
  
  <p>The dataframe only holds a single column at the moment and the length of each array in the values column is not strict.</p>
  
  <p>Expected output:</p>
  
  <pre><code>value                             average
  [0.0,12.34,223.12,4.55,...]        77.87
  [0.0,78.12,12.90,...]              12.11            
  .
  .
  . 
  </code></pre>
  
  <p>Np.mean() will not work when I try to loop through the dataframe using iterrows().</p>
  
  <p>Essentially I need to expand the code below to calculate all the averages in a dataframe:</p>
  
  <pre><code>np.mean(df_average_pace.paces[0])
  </code></pre>