Converting a vector of maps to a map of vectors

core.clj

(defn maps->map-of-vectors
  [maps]
  (let [base (zipmap (mapcat keys maps) (repeat []))]
    (apply merge-with conj base maps)))

test.clj

(deftest maps->map-of-vectors
  (testing "converting a vector of maps to a map of vectors"
    (is (= { :a [1,3] :b [2,4] }
           (maps->map-of-vectors [{:a 1 :b 2} {:a 3 :b 4}])))))