Efficient Rank Ordering of Nested Lists

[pablo.mitchell at gmail.com]

A naive approach to rank ordering (handling ties as well) of nested
lists may be accomplished via:

   def rankLists(nestedList):
      def rankList(singleList):
          sortedList = list(singleList)
          sortedList.sort()
          return map(sortedList.index, singleList)
      return map(rankList, nestedList)

   >>> unranked = [ [ 1, 2, 3, 4, 5 ], [ 3, 1, 5, 2, 4 ], [ -1.1, 2.2,
0, -1.1, 13 ] ]
   >>> print rankLists(unranked)

   [[0, 1, 2, 3, 4], [2, 0, 4, 1, 3], [0, 3, 2, 0, 4]]

This works nicely when the dimensions of the nested list are small.
It is slow when they are big.  Can someone suggest a clever way to
speed it up?