title: Adding an extra index to Pandas DataFrame
body: <p>I have a list of DataFrame, which is read something like this</p>
  
  <pre><code>data = [pd.read_csv(f, index_col=None, header=None) for f in temp]
  flow = pd.DataFrame(data)
  </code></pre>
  
  <p>If I print the <code>flow</code> I get an output of </p>
  
  <pre><code>[[....
  [128 rows x 14 columns]]
  [128 rows x 14 columns]]
  .
  .
  [128 rows x 14 columns]]]
  </code></pre>
  
  <p>So this means that each of the <code>[128 rows x 14 columns]</code> has one index, I have <code>60</code> as such. What I wanted to do was to read another CSV file which contains one column of data (60 rows) which looks something like this</p>
  
  <pre><code>[1 1 1 ... 2 2 2 ... 3 3 3]
  </code></pre>
  
  <p>I can read this by doing</p>
  
  <pre><code>new_data=pd.read_csv(f_new, index_col=None, header=None)
  </code></pre>
  
  <p>Now my question is can I keep everything as it is and just add the <code>new_data</code> as extra index, which should show something like this:</p>
  
  <pre><code>[[....
  0 1 [128 rows x 14 columns]]
  1 1 [128 rows x 14 columns]]
  2 1 .
  3 2 .
  4 2 [128 rows x 14 columns]]]
  </code></pre>
  
  <p>Is this possible?</p>