On Tue, Aug 26, 2008 at 11:54 PM, Shawn Hoover <[EMAIL PROTECTED]> wrote:
> For one thing, it seems like there must be a cleaner way to handle
> my use of reduce in test-shuffle-uniformity. I like reduce for
> looping functionally, but in this case I just need to run n times
> regardless of the specific values in (range n). Is that use case
> common enough for some kind of reduce-times macro?
I can't say I've needed such a thing very often. Your own
reduce-times macro might clarify your code a bit, though.
> (defn test-shuffle-uniformity
> "Shuffles a 3-item collection n times, mapping each result to the number of
> times it's hit. If the distribution isn't uniform we've let bias into the
> random numbers or the algorithm. Typical results on my machine:
> (2 1 3) : 16611
> (3 2 1) : 16771
> (1 3 2) : 16707
> (1 2 3) : 16766
> (3 1 2) : 16555
> (2 3 1) : 16590"
> ([n] (test-shuffle-uniformity n shuffle))
> ([n shuffle]
> (let [coll [1 2 3]
> results (reduce (fn [results _]
> (let [result (shuffle coll)]
> (assoc results result
> (inc (or (get results result)
> 0)))))
> {} (range n))]
> (doseq r results
> (println (key r) ":" (val r))))))
You could simplify your reduce fn a bit by using merge-with:
(defn test-shuffle-uniformity
"Shuffles a 3-item collection n times, mapping each result to the number of
times it's hit. If the distribution isn't uniform we've let bias into the
random numbers or the algorithm. Typical results on my machine:
(2 1 3) : 16611
(3 2 1) : 16771
(1 3 2) : 16707
(1 2 3) : 16766
(3 1 2) : 16555
(2 3 1) : 16590"
([n] (test-shuffle-uniformity n shuffle))
([n shuffle]
(let [coll [1 2 3]
results (reduce (fn [results _]
(merge-with + results {(shuffle coll) 1}))
{} (range n))]
(doseq r results
(println (key r) ":" (val r))))))
--Chouser
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