title: How to access DataFrame column created with DataFrame.groupby
body: <p>After creating a DataFrame with a column 'a' having the duplicated cell values:</p>
  
  <pre><code>import pandas as pd
  df = pd.DataFrame({'a': [1,2,2,3,3,3,3],
                     'b':[1,2,3,4,5,6,7],
                     'c':[8,9,10,11,12,13,14]})
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/OlBbV.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/OlBbV.png" alt="enter image description here"></a></p>
  
  <p>I proceed by creating a copy of it where I consolidate the duplicated cells in column 'a' while summing the values of other cells. I am using <code>groupby</code> method to achieve this, like so:</p>
  
  <pre><code>groupDf = df.groupby('a', axis=0).sum()
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/Pullb.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Pullb.png" alt="enter image description here"></a></p>
  
  <p>After the consolidated version of the DataFrame is created I want to access its columns ['a']:</p>
  
  <pre><code>print(groupDf['a])
  </code></pre>
  
  <p>and I am getting the <code>KeyError</code> notifying me that ['a'] column does not exist.
  Printing the column names with <code>groupDf.columns</code> returns only the column 'b' and the column 'c': <code>Index(['b', 'c'], dtype='object')</code></p>
  
  <p>How should I access the column 'a? </p>