Brilliant, thank you very much!
Nik
On Nov 16, 5:41 pm, Rich Hickey <[EMAIL PROTECTED]> wrote:
> On Nov 16, 12:18 pm, "Craig Andera" <[EMAIL PROTECTED]> wrote:
>
>
>
> > One way I could think of to do this would be to build a map with each
> > unique item as a key and the count as its value. Then it would be
> > trivial to pull out the keys with the count as a specified value. I
> > started writing this, but my SLIME is royally screwed up right now
> > after the upgrade to Clojure HEAD. Sorry. Anyway, it shouldn't require
> > any refs - probably just a loop/recur.
>
> > Or maybe someone has a far more clever idea. :)
>
> > > On Sun, Nov 16, 2008 at 12:02 PM, npt11tpn <[EMAIL PROTECTED]> wrote:
>
> > > Hi guys,
> > > This is my first post to the group, but have been following the
> > > discussions for almost a year. Many thanks to Rich Hickey for creating
> > > a fantastic future-proof language which is a pleasure to use and to
> > > the great community!
> > > The following function (as part of a chemistry-related application)
> > > filters the elements of a sequence that a repeated a specified number
> > > of times. Wondering if the function could be simplified and written
> > > without the reference (newseq).
> > > Thanks a lot!
> > > Nik
>
> > > (defn filter-repeats [seq n]
> > > "Returns a vector of the elements of a sequence that are repeated n
> > > times"
> > > (let [newseq (ref [])]
> > > (doseq [u (set seq)]
> > > (when (= (count (filter #(= % u) seq)) n)
> > > (dosync (commute newseq conj u))))
> > > [EMAIL PROTECTED]))
>
> > > Usage e.g.
> > > (filter-repeats '(2 3 1 4 2 2 4 3 5 ) 2)
> > > [3 4]
>
> (defn filter-repeats [n coll]
> (let [counts (reduce (fn [m k] (assoc m k (inc (m k 0))))
> {} coll)]
> (for [[k v] counts :when (= v n)] k)))
>
> Rich
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