I don't know if this is *clearer* than the reduce version ...
user> (def xs [1 3 4 5 7 9 10 11 12 ])
#'user/xs
user> (defn consecutivizer []
(let [prev (atom nil)
last-returned (atom (gensym))]
(fn [cur]
(when-not (or (nil? @prev)
(= (inc @prev) cur))
(reset! last-returned (gensym)))
(reset! prev cur)
@last-returned)))
#'user/consecutivizer
user> (partition-by (consecutivizer) xs)
((1) (3 4 5) (7) (9 10 11 12))
On Thu, Nov 6, 2014 at 5:10 PM, Gordon Stratton <[email protected]>
wrote:
> On Thu, Nov 6, 2014 at 10:22 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))
> > ~~~
> >
> > Can anyone suggest a better / simpler / more easily-understandable way
> to do
> > this in Clojure?
>
> Hey John,
>
> I think your approach is pretty good. I made some small modifications:
>
> (defn congeal-consecutives
> [xs]
> (if (empty? xs)
> []
> (reduce (fn [acc x]
> (let [l (last acc)]
> (if (= (inc (last l)) x)
> (conj (pop acc) (conj l x))
> (conj acc [x]))))
> [[(first xs)]]
> (rest xs))))
>
> I didn't see how to use `partition-by` in a way that made the function
> any clearer than the `reduce` version, but I'd be interested if you or
> others do.
>
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--
Ben Wolfson
"Human kind has used its intelligence to vary the flavour of drinks, which
may be sweet, aromatic, fermented or spirit-based. ... Family and social
life also offer numerous other occasions to consume drinks for pleasure."
[Larousse, "Drink" entry]
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