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From Matt Lyon <>
Subject Re: ranking a big list
Date Sun, 07 Feb 2010 00:58:47 GMT
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

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