title: How can I extract a column from dataframe and attach it to rows while keeping other columns intact
body: <p>How can I extract a column from pandas dataframe attach it to rows while keeping the other columns same.</p>
  
  <p>This is my example dataset.</p>
  
  <pre><code>import pandas as pd
  import numpy as np
  df = pd.DataFrame({'ID':  np.arange(0,5),
                    'sample_1' : [5,6,7,8,9],
                    'sample_2' : [10,11,12,13,14],
                    'group_id' : ["A","B","C","D","E"]})
  </code></pre>
  
  <p>The output I'm looking for is:</p>
  
  <pre><code>df2 = pd.DataFrame({'ID':  [0, 1, 2, 3, 4, 0, 1, 2, 3, 4],
                    'sample_1' : [5,6,7,8,9,10,11,12,13,14],
                    'group_id' : ["A","B","C","D","E","A","B","C","D","E"]})
  </code></pre>
  
  <p>I have tried to slice the dataframe and concat using <code>pd.concat</code> but it was giving NaN values. </p>
  
  <p>My original dataset is large.</p>