core.clj

(require '[clojure.zip :as zip])

(defn ->zipper [data]
  (zip/zipper (fn [[_ x]]
                (coll? x))
              (fn [[_ x]]
                (if (map? x)
                  (seq x)
                  (map vector (range) x)))
              nil
              [nil data]))

(defn squash [data]
  (loop [z (-> data ->zipper zip/next)
         r {}]
    (if (zip/end? z)
      r
      (let [[k v] (zip/node z)]
        (if (coll? v)
          (recur (zip/next z) r)
          (let [path (->> z
                          zip/path
                          (rest)
                          (mapv first))]
            (recur (zip/next z) (assoc r (conj path k) v))))))))

(squash {:foo {:bar [{:a 1} {:a 2}]}})

{[:foo :bar 0 :a] 1, [:foo :bar 1 :a] 2}