like this:
(defn shuffle-java ;;from Shawn Hoover post on these google groups
"Shuffles coll using a Java ArrayList. Blows shuffle out of the
water on speed and space."
[coll]
(let [l (java.util.ArrayList. coll)]
(java.util.Collections/shuffle l)
(seq l)))
(defn random-number-list [max dim]
(take dim (shuffle-java (range 0 max))))
user> (random-number-list 100 20)
(38 70 73 57 10 81 32 99 92 19 77 39 27 24 47 17 86 8 58 76)
On Aug 25, 1:30 pm, Jonathan Smith <jonathansmith...@gmail.com> wrote:
> Why not make a list of numbers from 0 to max, randomly shuffle it,
> and do a take on the resulting sequence until you have enough numbers.
>
> On Aug 25, 10:16 am, sebastien <sebastien....@gmail.com> wrote:
>
> > What is the most efficient way to generate list of unique random
> > numbers? The function must look something like this:
>
> > (defn make-random-numbers [dim max]
> > ....)
>
> > where dim is dimensionality of the vector, and max is the upper bound
> > of random numbers.
> > The problem is not to allow duplicates in the sequence. I've found two
> > options to solve this task:
> > 1) the most straightforward way is to check if sequence already
> > contains new element on every addition, but it requires O(n!) steps
> > for a list of n numbers;
> > 2) using clojure sets will make it easy to add unique numbers, but it
> > will return sorted sequence, so i need to shuffle it by myself, and i
> > don't see efficient way to do this.
>
> > So, is there any other ways to do the task?
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