Difference between two maps

Question

I need to very efficiently compare two maps in Clojure/Java, and return the difference as determined by Java\'s .equals(..), with nil/null equivalent to \"not present\".

Answer 1

I am not sure about its performance

(defn map-difference
  [orig other]
  (let [changed (set/difference (set orig) (set other))
        added (set/difference (set (keys other)) (set (keys orig)))]
    (reduce (fn [acc key]
              (assoc acc key :missing))
      (into {} changed)
      added)))

I used :missing key to avoid ambiguity between a nil value in the original map, and a missing key -- you can of course change it to nil.