title: pandas align() function : illustrative example
body: <p>I came across this line of code</p>
  
  <pre><code>app_train_poly, app_test_poly = app_train_poly.align(app_test_poly, join = 'inner', axis = 1)
  </code></pre>
  
  <p>here <em>app_train_poly</em> and <em>app_test_poly</em> are the pandas dataframe.</p>
  
  <p>I know that with <em>align()</em> you are able to perform some sort of combining of the two dataframes but I am not able to visualize how does it actually work.</p>
  
  <p>I searched the documentation but could not find any illustrative example.</p>