title: Comparing two lists of strings and getting indices of duplicates
body: <p>I want to get the indices of the values (strings) which are duplicated. 
  For example:</p>
  
  <pre><code>a=['iii','jjj','rrr']
  b=['iii','lll','yyy','ttt','jjj']    
  s=numpy.where(a==b)
  </code></pre>
  
  <p>I want <code>s</code> to return <code>[0,4]</code>, but at the moment it just returns <code>[0]</code> as this is where they are the same value and in same position in the list.</p>