I would try to avoid last and but-last as they work in linear time. How about
something like this?
(defn congeal-consecutives [coll]
(when (seq coll)
(let [[_ group res] (reduce (fn [[succ group res] n]
(if (== succ n)
[(inc n) (conj group n) res]
[(inc n) [n] (conj res group)]))
[(nth coll 0) [] []]
coll)]
(conj res group))))
> On Nov 6, 2014, at 5:22 PM, John Gabriele <[email protected]> wrote:
>
> Hi all,
>
> I've got this: `[1 3 4 5 7 9 10 11 12]`
> and I'd like to turn it into this: `[[1] [3 4 5] [7] [9 10 11 12]]`.
>
> That is, I'd like to group consecutive numbers together (the final goal being
> to produce something like `["1" "3-5" "7" "9-12"]`, but that's the easy part).
>
> I haven't found an easy way to do this. Here's what I've come up with in
> Clojure:
>
> ~~~clojure
> #!/usr/bin/env lein-exec
>
> (def v [1 3 4 5 7 9 10 11 12])
>
> (defn congeal-consecutives
> [coll]
> (reduce (fn [accum x]
> (if (= x (inc (last (last accum))))
> (concat (butlast accum)
> [(conj (last accum) x)])
> (concat accum
> [[x]])))
> [[(first coll)]]
> (rest coll)))
>
> (prn (congeal-consecutives v))
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