title: openpyxl concat three dataframes horizonally
body: <p>I am using <code>openpyxl</code> to edit three <code>dataframes</code>, <code>df1, df2, df3</code> (If it is necessary, we can also regard as three excels independently):</p>
  <pre><code>import pandas as pd
  
  data1 = [[1, 1],[1,1]]
  df1 = pd.DataFrame(data1, index = ['I1a','I1b'], columns=['v1a', 'v1b'])
  df1.index.name='I1'
  
  data2 = [[2, 2,2,2],[2,2,2,2],[2,2,2,2],[2,2,2,2]]
  df2 = pd.DataFrame(data2, index = ['I2a','I2b','I2c','I2d'], columns=['v2a','v2b','v2c','v2d'])
  df2.index.name='I2'
  
  data3 = [['a', 'b',3,3],['a','c',3,3],['b','c',3,3],['c','d',3,3]]
  df3 = pd.DataFrame(data3, columns=['v3a','v3b','v3c','v3d'])
  df3 = df3.groupby(['v3a','v3b']).first()
  </code></pre>
  <p><a href="https://i.stack.imgur.com/tBdFJ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/tBdFJ.png" alt="enter image description here" /></a></p>
  <p>Here df3 is <code>multiindex</code>. How to concat them into one excel horizontally (each dataframe start at the same line) as following:</p>
  <p><a href="https://i.stack.imgur.com/GTNXd.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/GTNXd.png" alt="enter image description here" /></a></p>
  <p>Here we will regard index as a column and for <code>multiindex</code>, we keep the first level hidden.</p>