title: How to get the intersection of two dataframes?
body: <p>I have two dataframes of similar format:</p>
  
  <pre><code>df1 = DataFrame({'a':[0,1,2,3,4], 'b':['q','r','s','t','u']})
  df1
  
      a   b
  0   0   q
  1   1   r
  2   2   s
  3   3   t
  4   4   u
  
  df2 = DataFrame({'a':[4,3,2,1,999], 'b':['u','r','s','t','u']})
  df2
  
      a   b
  0   4   u
  1   3   r
  2   2   s
  3   1   t
  4   999 u
  </code></pre>
  
  <p>I would like to get a new dataframe that has rows that appear in both of these (ignoring the index). So the above example gives a dataframe</p>
  
  <pre><code>    a   b
  0   4   u
  1   2   s
  </code></pre>
  
  <p>How do I get this intersection?</p>