title: how to flatten array in pandas dataframe
body: <p>Assuming I have a pandas dataframe such as</p>
  
  <pre><code>df_p = pd.DataFrame(
     {'name_array':
      [[20130101, 320903902, 239032902],
       [20130101, 3253453, 239032902],
       [65756, 4342452, 32425432523]],
      'name': ['a', 'a', 'c']} )
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/6Za3m.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/6Za3m.png" alt="Image of dataframe"></a></p>
  
  <p>I want to extract the series which contains the flatten arrays in each row whilst <strong>preserving the order</strong> </p>
  
  <p>The expected result is a <code>pandas.core.series.Series</code></p>
  
  <p><a href="https://i.stack.imgur.com/CfSje.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/CfSje.png" alt="Image of expected output"></a></p>
  
  <p>This question is not a duplicate because my expected output is a pandas Series, and not a dataframe.</p>