On Tue, Dec 27, 2011 at 2:03 PM, endbegin <nkripl...@gmail.com> wrote:
> Hi,
>
> I am new to learning clojure, and I am hoping there is a solution to
> something that is not obvious to me ... I have a function that I want
> to run multiple times, measure the time it takes to execute each
> function, and put those numbers in a vector. I would like to process
> that vector further by doing things like max, min and average, and I
> think I can do that fairly "easily", but I'm having trouble generating
> such a vector in the first place.
>
> For instance when I do this:
>
> => (dorun (repeatedly 3 myfunc))
>
> I get
>
> "Elapsed time: 1253.764 msecs"
> "Elapsed time: 20003.997 msecs"
> "Elapsed time: 653.919 msecs"
> nil
>
> I would like to get something like
> [1253.764 200003.997 653.919], which I can post-process.
>
> I tried a
>
> => (conj [] (dorun (repeatedly 3 myfunc)))
>
> but that just gives me a [nil].
>
> Can anyone help?
>
> Thanks ...
The time macro *prints* the time rather than *returning* it. It
returns whatever the timed thing returned. For some purposes, such as
yours, that is unfortunate. You may want to use something like this:
(defmacro bench
"Times the execution of forms, discarding their output and returning
a long in nanoseconds."
([& forms]
`(let [start# (System/nanoTime)]
~@forms
(- (System/nanoTime) start#))))
(untested) where you'd be able to gather results in a seq by methods like this:
user=> (repeatedly 3 #(bench (foo) (bar)))
(483458232 483458419 483457443)
HTH.
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