title: How to concatenate two dataframes without duplicates?
body: <p>I'd like to concatenate two dataframes <code>A</code>, <code>B</code> to a new one without duplicate rows (if rows in <code>B</code> already exist in <code>A</code>, don't add):</p>
  <p>Dataframe <code>A</code>:</p>
  <pre><code>   I    II   
  0  1    2    
  1  3    1    
  </code></pre>
  <p>Dataframe <code>B</code>:</p>
  <pre><code>   I    II
  0  5    6
  1  3    1
  </code></pre>
  <p>New Dataframe:</p>
  <pre><code>     I    II
    0  1    2
    1  3    1
    2  5    6
  </code></pre>
  <p>How can I do this?</p>