title: How to concatenate two dataframes with different indices along column axis
body: <p>I want to merge 2 dataframes and first is <code>dm.shape = (21184, 34)</code>, second is <code>po.shape = (21184, 6)</code>. I want to merge them then it will be 40 columns. I write as this</p>
  
  <pre><code>dm = dm.merge(po, left_index=True, right_index=True)
  </code></pre>
  
  <p>then it is <code>dm.shape  = (4554, 40)</code> my rows decreased.</p>
  
  <p>P.s <code>po</code> is the <code>PolynomialFeatures</code> of numerical data of <code>dm</code>.</p>