title: Pandas: How to concatenate dataframes with different columns?
body: <p>I tried to find the answer in the official <a href="http://pandas.pydata.org/pandas-docs/stable/merging.html" rel="noreferrer">Pandas documentation</a>, but found it more confusing than helpful. Basically I have two dataframes with overlapping, but not identical column lists:</p>
  
  <pre><code>df1:
     A   B
  0  22  34
  1  78  42
  
  df2:
     B   C
  0  76  29
  1  11  67
  </code></pre>
  
  <p>I want to merge/concatenate/append them so that the result is</p>
  
  <pre><code>df3:
     A   B   C
  0  22  34  nan
  1  78  42  nan
  2  nan 76  29
  3  nan 11  67
  </code></pre>
  
  <p>Should be fairly simple, but I've tried several intuitive approaches and always got errors. Can anybody help me?</p>