title: how to append two columns in a dataframe side by side in pandas
body: <p>I have a dataframe input called <code>df_final</code> that looks like below:</p>
  <pre><code> location      2022-01   2022-02    2022-03   2022-01   2022-02  2022-03  
        AGH      2062.25   6561.43   3154.43     0        0        0
        AIM      3122.74   3277.56   3631.45     0        0        0
        AJL      1641.82   3229.49   4937.23     0        0        0
   .................
  </code></pre>
  <p>The first batch of months(first three column months) are actually the total cost while the last three columns are actually the total CN. My code to generate this output is like below:</p>
  <pre><code># Get monthly delivery CN
      total_delivery_CN = monthly_delivery_CN_by_branch(start_date, end_date)
      
    # Get monthly pickup CN
      total_pickup_CN = monthly_pickup_CN_by_branch(start_date, end_date)
  
    # Get monthly maintainence cost:
      total_maintainence_cost = monthly_maintainence_cost_by_branch(start_date, end_date)
  
    # Get monthly refuel cost:
      total_refuel_cost = monthly_refuel_cost_by_branch(start_date, end_date)
      
    # Union 
      df = pd.concat([total_delivery_CN, total_pickup_CN, total_maintainence_cost, total_refuel_cost])
      print('Union')
      print(df)
      df.to_csv('df.csv')
      
    # Pivot
      df_final = df.pivot_table(index=['location'], columns = ['report_month'], aggfunc = {'total_CN' : np.sum, 'Cost' : np.sum} , fill_value=0)
      
      df_final.columns = df_final.columns.to_flat_index().to_series().apply(lambda x: x[1])
      df_final = df_final.reset_index()
      df_final.to_csv('df_final.csv')
      
      print(df_final)
  </code></pre>
  <p>However, I would one to merge the two total's under the same month so the final output would look like:</p>
  <pre><code>                    2022-01                  2022-02                  2022-03       
       location     Cost     total_CN      Cost     total_CN       Cost     total_CN
        AGH        2062.25     0            6561.43     0          3154.43      0                 
        AIM        3122.74     0            3277.56     0          3631.45      0               
        AJL        1641.82     0            3229.49     0          4937.23      0               
   .................
  </code></pre>
  <p>How do I append these two total's under the same month?</p>