Question

I came across a thing I needed today where I wanted to progressively associate entries in a map, each based on the results of the previous one(s). Here’s what I did:

(defn -Y [v k f] (assoc v k (f v)))

(defn build-map [a-map]
 (-> a-map
  (-Y :x #(reduce + (:values %) )  )
  (-Y :y #(/ (:x %) 100) )
  (-Y :z #(* (:y %) 10000000) )
 )
)
(build-map {:values (range 8)})

I’d welcome your thoughts on a) is it a good thing ? b) is there an existing way to do it that I haven’t seen ? (I don’t know the API well)

Answer 1

So you got a map that goes through some transformations and you end up with a final map. Your implementation looks fine to me except that -Y isn’t doing much of thing and it may not be required as a separate function.

You can do all this using just reduce function, something like:

(def operations [ [:x #(reduce + (:values %))]    
                  [:y #(/ (:x %) 100)]      
                  [:z #(* (:y %) 10000000)]    
                ])

(defn build-map [a-map]
   (reduce (fn [s [k f]] (assoc s k (f s) ) ) a-map operations)
   )

(build-map {:values (range 8)})