A couple more updates to these:
> (defn random-permutation [s]
> "Return a random permutation of this seq."
> (let [arr (to-array s) len (alength arr)]
> (dotimes [i (dec len)]
> (let [r (+ i (rand-int (- len i))),
> prev (aget arr i)]
> (aset arr i (aget arr r))
> (aset arr r prev)))
> (seq arr)))
Per [1] this thread,
(defn shuffle-java
"Shuffles coll using a Java ArrayList. Blows shuffle out of the
water on
speed and space."
[coll]
(let [l (ArrayList. coll)]
(Collections/shuffle l)
(seq l)))
is both much simpler and much much much faster than my implementation.
[1] http://groups.google.com/group/clojure/browse_thread/thread/180842eb58c58370
> (defmacro lazy-get "Like get but lazy about evaluating the default
> value"
> [m k d]
> `(if-let [pair# (find ~m ~k)]
> (second pair#)
> ~d))
This should be
(defmacro lazy-get "Like get but lazy about evaluating the default
value"
[m k d]
`(if-let [pair# (find ~m ~k)]
(val pair#)
~d))
Changing the "second" to a "val" speeds both this and safe-get up by
more than a factor of 4! [2]
[2] http://w01fe.com/blog/2009/01/more-on-clojure-map-accessor-speeds/
Also, once again (Chouser?), is there anything I can do to help
implement the changes we've talked about? I can try to make patches
for the changes in core, and/or improve and document other utilities
for clojure.contrib, if that would be helpful.
Cheers,
Jason
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