Hi John,
As miner mentioned, peek is preferable to last for vectors. Here is an
implementation based on the observation that consecutive increasing numbers
are equivalent when you subtract their indices. Maybe it is more clever
than simple.
(ns experimental-clojure.congeal-consecutives)
(def v [1 3 4 5 7 9 10 11 12])
(defn congeal-consecutives [coll]
(->> coll
(map-indexed (fn [i x] [(- x i) x]))
(partition-by first)
(mapv (fn [pairs]
(mapv second pairs)))))
(defn rangify [coll]
(mapv (fn [r]
(assert (vector? coll))
(let [f (first r)
top (peek r)]
(if (= f top)
(str f)
(str f "-" top)))) coll))
(-> v
congeal-consecutives
rangify)
https://gist.github.com/johnwalker/8e7e6a8bcbeff03d4e80
On Thursday, November 6, 2014 2:22:14 PM UTC-8, John Gabriele 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))
> ~~~
>
> and here's it done in Python:
>
> ~~~python
> #!/usr/bin/python3
>
> v = [1, 3, 4, 5, 7, 9, 10, 11, 12]
>
> def congeal_consecutives(coll):
> accum = [[ coll[0] ]]
> more = coll[1:]
> for x in more:
> if x == accum[-1][-1] + 1:
> accum[-1].append(x)
> else:
> accum.append([x])
> return accum
>
> print(congeal_consecutives(v))
> ~~~
>
> Can anyone suggest a better / simpler / more easily-understandable way to
> do this in Clojure?
>
> Thanks,
> -- John
>
>
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