map-in

[Steve Ashton]

Is there anything for map which operates like update-in and assoc-in, where we can call a function with the value looked up in a nested structure?

What I've come up with:

(defn map-in

  "Returns a lazy sequence consisting of the results of

  calling map on coll, for each value in the coll,

  extracting the value using keys ks, finally applying f the

  that value and args: (apply f item args)"

  [coll [& ks] f & args]

  (map (fn [item]

         (let [value (reduce #(%2 %1) item ks)]

           (apply f value args)))

       coll))

Which could then be used like:

(def customers [{:name "Alice" :address {:city "Raleigh" :state "NC"}}

                {:name "Bob" :address   {:city "Seattle" :state "WA"}}])

(map-in customers [:address :state] #(-> % clojure.string/lower-case keyword))

=> (:nc :wa)

Just wondering if I am re-inventing something here.

Thanks,

Steve

[Francis Avila]

The reduce in your mapped function is already implemented by get-in. Other possible implementations using get-in:

(defn map-in [coll ks f & args]
  (->> coll
       (map #(get-in % ks))
       (map #(apply f % args))))

Or:

(defn map-in [coll ks f & args]
  (map #(apply f (get-in % ks) args) coll))