FWIW, what you're doing here is a statistical analysis called a percentile rank. In what I'm doing, for any given set of sums, I want to know which quadrile [0-25/26-50/51-75/76-100] of all the sums any particular sum is in. I can't necessarily tell you how to do this in javascript because I'm interacting with couchdb from ruby anyway and using a ruby library (array_statistics) to do this kind of analysis on a simple sum reduce from couch, but hopefully this will point you in the right direction. On Sat, Feb 6, 2010 at 5:00 AM, Mano wrote: > Hi, > > I have a large list of assessment scores (of about 500k students). The > scores can range between 0 and 200. How do I find the rank of a particular > score? For smaller lists, I can just sort the array of scores and for each > student's score I can get the index of their score in the sorted list. But > how do I achieve it using mapreduce? > > Thanks, > mano > > -- > Lord, give us the wisdom to utter words that are gentle and tender, for > tomorrow we may have to eat them. >   -Sen. Morris Udall >