This works, assuming xs consists of positive integers:
(define (benford xs)
(for-each
(lambda (x) (printf "~a ~f~%" (car x) (/ (cdr x) (length xs))))
(uniq-c = (sort < (map (compose car digits) xs)))))
Compose, digits and uniq-c are from my Standard
Prelude<http://programmingpraxis.com/standard-prelude>
.
Phil
On Wed, Oct 13, 2010 at 11:10 PM, Shriram Krishnamurthi
<s...@cs.brown.edu>wrote:
> Given: A list of numbers. Assume integers (though it isn't necessary
> for the underlying issue).
>
> Task: To determine how often the first digit is 1, the first digit is
> 2, ..., the first digit is 9, and present as a table. You may exploit
> DrRacket's pretty-printer, e.g., by using a list of lists:
>
> '((#\1 22.51539138082674)
> (#\2 16.44678979771328)
> (#\3 15.567282321899736)
> (#\4 12.401055408970976)
> (#\5 9.058927000879507)
> (#\6 7.651715039577836)
> (#\7 6.420404573438875)
> (#\8 5.804749340369393)
> (#\9 4.133685136323659))
>
> I leave the precise format of the output unstated so you're free to
> choose a clever representation; your answer should be at least as
> visually clear as the above.
>
> You should not mutate the original list, since it may be necessary for
> other computations.
>
> Smallest/tightest/cleanest/best?
>
> Shriram
>
> PS: Of course, this is to explore Benford's Law:
>
> http://en.wikipedia.org/wiki/Benford's_law
>
> which is the subject of my lecture tomorrow. The above
> distribution is from the size of the littoral zone (in acres) of
> the lakes of Minnesota.
>
> PPS: If you really want to you can assume the data are actually in a
> CSV file (as mine are -- thanks, Neil!), in case you can come up
> with something even cleverer.
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