title: Clustering a huge number of URLs
body: <p>I have to find similar URLs like</p>
  
  <p>'<a href="http://teethwhitening360.com/teeth-whitening-treatments/18/" rel="nofollow">http://teethwhitening360.com/teeth-whitening-treatments/18/</a>'<br>
  '<a href="http://teethwhitening360.com/laser-teeth-whitening/22/" rel="nofollow">http://teethwhitening360.com/laser-teeth-whitening/22/</a>'<br>
  '<a href="http://teethwhitening360.com/teeth-whitening-products/21/" rel="nofollow">http://teethwhitening360.com/teeth-whitening-products/21/</a>'
  '<a href="http://unwanted-hair-removal.blogspot.com/2008/03/breakthroughs-in-unwanted-hair-remo" rel="nofollow">http://unwanted-hair-removal.blogspot.com/2008/03/breakthroughs-in-unwanted-hair-remo</a>'<br>
  '<a href="http://unwanted-hair-removal.blogspot.com/2008/03/unwanted-hair-removal-products.html" rel="nofollow">http://unwanted-hair-removal.blogspot.com/2008/03/unwanted-hair-removal-products.html</a>'<br>
  '<a href="http://unwanted-hair-removal.blogspot.com/2008/03/unwanted-hair-removal-by-shaving.ht" rel="nofollow">http://unwanted-hair-removal.blogspot.com/2008/03/unwanted-hair-removal-by-shaving.ht</a>'  </p>
  
  <p>and gather them in groups or clusters. My problems:</p>
  
  <ul>
  <li>The number of URLs is large (1,580,000)</li>
  <li>I don't know which clustering or method of finding similarities is better</li>
  </ul>
  
  <p>I would appreciate any suggestion on this.</p>