By the way, I also noticed your logic is wrong. It should be (+ (* i
ncol) j) rather than (* i j).
-Per
On Tue, Mar 9, 2010 at 2:57 AM, Jonathan Shore <jonathan.sh...@gmail.com> wrote:
> Hi,
> I'm still trying to work out the best way to deal with operations on
> heterogenous data in clojure. I have a complex application which has such
> requirements. I wrote a simple toy matrix as a means to explore closure
> versus map based implementations. Note that in this case the "data
> structure" is not pure, rather mutable. Here are 2 implementations I came
> up with (note this is my second day with closure, so my not be idiomatic):
> The first impl uses closures and provides access via a function (is there a
> more efficient way to do this?, avoiding the cond-dispatch?):
>
> (defn matrix-1 [nrow ncol]
> (let [data (float-array (* nrow ncol))]
> (fn [command & args]
> (condp = command
> :dim
> [nrow ncol]
> :get
> (let [[i j] args] (aget data (* i j)))
> :set
> (let [[i j v] args] (aset-float data (* i j) v))))))
>
> The second implementation uses a map:
> (defn matrix-2 [nrow ncol]
> { :data (float-array (* nrow ncol)), :nrow nrow, :ncol ncol })
> (defn mset! [mat i j v]
> (aset-float (get mat :data) (* i j) v))
> (defn mget [mat i j]
> (aget (get mat :data) (* i j)))
>
> (defn mdim [mat]
> [(get mat :nrow) (get mat :ncol)])
> Both of these implementations bother me. The first because of the dispatch,
> the second because maps clearly are not "near the metal". It would seem
> would have to resort to java side classes, unless there is a better way?
> BTW, the map implementation is about 3x faster:
> (def m1 (matrix-1 10 10))
> (def m2 (matrix-2 10 10))
> ...
> (defn benchmark [what times f]
> (let [
> Tstart
> (System/currentTimeMillis)
> result
> (loop [ntimes times]
> (f)
> (if (> ntimes 0)
> (recur (- ntimes 1))))
> Tend
> (System/currentTimeMillis)]
> (println "evaluating" what "took" (- Tend Tstart) "ms")))
> (benchmark "map-based-matrix" 1000000 (fn [] (mset! m2 3 3 0.1234)))
> (benchmark "closure-based-matrix" 1000000 (fn [] (m1 :set 3 3 0.1234)))
>
>
>
>
>
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