title: Select rows if combination of columns are from other data frame in Python Pandas
body: <p>I have a large data frame with Origin, Destination and other data points. How do I efficiently select rows that have the Origin, Destination pairs of interest, i.e. I have another data frame with the pairs of interest.</p>
  
  <pre><code>df = pd.DataFrame({'Origin' : ['A','A','A','B','B','A'], 
                     'Destination' :['B','C','D','C','D','D'], 
                     'X' : ['a','b', 'c', 'd', 'e', 'f']})
  
  
  I = pd.DataFrame({'Origin' : ['A','A','B'], 'Destination' : ['B','D','C']})
  </code></pre>
  
  <p>And I would want to return back </p>
  
  <pre><code>  Origin Destination  X
  0      A           B  a
  1      A           D  c
  2      B           C  d
  3      A           D  f
  </code></pre>