clojure invert multi-valued map

invert_map.clj

(defn invert-map [m]
  (reduce-kv
   (fn [acc k v]
     (merge-with (comp vec concat)
                 acc
                 (apply array-map (interleave v (repeat [k])))))
   {} m))

(invert-map {:a [:foo :bar] :b [:baz] :c [:baz]})
;; => {:baz [:c :b], :bar [:a], :foo [:a]}