title: Count the duplicates in a list of tuples
body: <p>I have a list of tuples: <code>a = [(1,2),(1,4),(1,2),(6,7),(2,9)]</code> I want to check if one of the individual elements of each tuple matches the same position/element in another tuple, and how many times this occurs.</p>
  
  <p>For example: If only the 1st element in some tuples has a duplicate, return the tuple and how many times it's duplicated.
  I can do that with the following code:</p>
  
  <pre><code>a = [(1,2), (1,4), (1,2), (6,7), (2,9)]
  
  coll_list = []
  for t in a:
      coll_cnt = 0
      for b in a:
          if b[0] == t[0]:
              coll_cnt = coll_cnt + 1
      print "%s,%d" %(t,coll_cnt)
      coll_list.append((t,coll_cnt))
  
  print coll_list
  </code></pre>
  
  <p>I want to know if there is a more effective way to do this?</p>