The seq-utils library has a shuffle function that calls out to
java.util.Collections.
If you want to do it yourself, the easiest would be
(defn naive-shuffle [xs]
(let [v (vec xs)]
(->> (count v) range lex-permutations rand-elt (map v))))
This uses the seq-utils and combinatorics libraries from clojure.contrib.
However, generating all permutations obviously doesn't scale beyond a
couple of elements. For that you will need a real algorithm like the
Knuth shuffle:
(defn swap-elts [x i j]
(assoc x i (x j) j (x i)))
(defn rand-range
([n] (rand-int n))
([m n] (+ m (rand-int (- n m)))))
(defn knuth-shuffle [xs]
(let [v (vec xs)]
(reduce #(swap-elts %1 %2 (rand-range %2 (count %1))) v (range (count v)))))
-Per
On Mon, Apr 5, 2010 at 3:14 AM, Linus Ericsson
<[email protected]> wrote:
> Hello Clojure!
>
> Is there any straight-forward way to randomly reorder a list?
>
> ie:
>
> (randomize-list (list 1 2 3 4))
> -> (3 2 1 4)
>
> Regards,
> Linus Ericsson
>
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