It was fun to try a naive implementation

(defn combine [m1 m2]
  (let [mm1 (transient m1)]
    (do
      (doseq [k (keys m2)]
        (if (contains? m1 k)
          (assoc! mm1 k (conj (mm1 k) (m2 k)))
          (assoc! mm1 k (m2 k))))
      (persistent! mm1))))



On 25/04/13 16:29, Cedric Greevey wrote:
Seems you want a cross between update-in and merge. Maybe something like this?

(defn combine
  "Merge maps, recursively merging nested maps whose keys collide."
  ([] {})
  ([m] m)
  ([m1 m2]
    (reduce (fn [m1 [k2 v2]]
              (if-let [v1 (get m1 k2)]
                (if (and (map? v1) (map? v2))
                  (assoc m1 k2 (combine v1 v2))
                  (assoc m1 k2 v2))
                (assoc m1 k2 v2)))
            m1 m2))
  ([m1 m2 & more]
    (apply combine (combine m1 m2) more)))

(warning: scarcely tested much)



On Thu, Apr 25, 2013 at 4:41 PM, Joachim De Beule <joachim.de.be...@gmail.com <mailto:joachim.de.be...@gmail.com>> wrote:

    Hi list,

    I was searching for an "easy" way to combined nested maps, e.g. as in

    (combine {:foo {:bar "baz"}} {:foo {:x "y"}})
    => {:foo {:bar "baz", :x "y"}}

    I would expect that there is some core map operation to do this,
    but neither merge nor unify work as they simply return {:foo {:x
    "y"}}, and I don't see anything else. Am I missing something?

    Joachim.
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