How about this:
(defn to-consolidated-map [parts]
(apply merge-with concat
(map (fn [[k v]] {k (list v)}) parts)))
On Fri, Aug 16, 2013 at 9:57 PM, David Chelimsky <dchelim...@gmail.com> wrote:
> I've got a vector of 2-element vectors e.g. [[:a 1] [:b 2]] where the first
> val of any vec might appear in another vec e.g. [[:a 1] [:b 2] [:a 3]]. I
> need a fn that will consolidate this into a hash-map with the vals
> consolidated e.g.
>
> (to-consolidated-map [[:a 1] [:b 2] [:a 3]])
> ; {:a 4 :b 2}
>
> I've got two candidate implementations and I'm curious which you like better
> and why, or if I'm missing a better way:
>
> (defn to-consolidated-map [parts]
> (reduce (fn [h [k v]]
> (if (contains? h k)
> (assoc h k (+ (k h) v))
> (assoc h k v)))
> {} parts))
>
> (defn to-consolidated-map [parts]
> (->> parts
> (group-by first)
> (map (fn [[k v]] [k (->> v (map last) (reduce +))]))))
>
> TIA,
> David
>
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