On Feb 3, 8:55 pm, braver <[email protected]> wrote:
> Meikel -- cool lazy solution, but doesn't generalize to replace <=
> with a predicate. Here's my non-lazy, reduce-based one generic with
> instantiations:
>
> (defn clis-pred
> [pred s]
> (let [[x & xs] s [r zs _]
> (reduce (fn [[r zs z] e]
> (if (pred z e) [r (conj zs e) e] [(conj r zs) [e] e]))
> [[] [x] x] xs)] (conj r zs)))
>
> (def clis-incr (partial clis-pred <))
> (def clis-nondecr (partial clis-pred <=))
> (def clis-nonincr (partial clis-pred >=))
> (def clis-decr (partial clis-pred >))
>
> Cheers,
> Alexy
If your input is a vector, the following will do the trick (relies on
subvec):
(use 'clojure.contrib.seq-utils)
(defn clis-pred [pred vec]
(->> vec
(partition 2 1)
(map reverse)
(map (partial reduce pred))
(cons false)
(positions false?)
(partition-all 2 1)
(map (partial apply subvec vec))))
In the general case, partition-by can be used:
(use 'clojure.contrib.seq-utils)
(defn clis-pred [pred seq]
(->> seq
(partition 2 1)
(reductions (fn [id [prev curr]] (if (pred curr prev) id (+ id
1))) 0)
(map vector seq)
(partition-by second)
(map (partial map first))))
Cheers,
Carlos
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