Not sure I follow Colin's suggestion entirely, but his suggestion led me to
this which is better. I'd still love any other suggestions to improve!
(def entities [{:name "foo" :location "us"} {:name "bar" :location "de"}])
(def locations [{:location "us" :id 100} {:location "de" :id 101}])
;; make an intermediary locations into a large single map of format {"us"
100 "de" 101}
(def locations* (apply hash-map (mapcat vals locations)))
(map #(assoc % :location (get locations* (:location %))) entities)
=> ({:name "foo", :location 100} {:name "bar", :location 101})
On Sunday, September 13, 2015 at 10:56:14 AM UTC-4, Colin Yates wrote:
>
> I would transform the locations into {location id} and then use merge.
>
> On 13 Sep 2015, at 3:14 PM, Brian Platz <bpl...@gmail.com <javascript:>>
> wrote:
>
> I have a pattern that comes up frequently, when I need to merge some value
> into one map list from matching keys in a second map list.
>
> I've developed a way to handle it, but I think it could be better. Here is
> a simple example of it:
>
> In the below case, we are looking to replace the :location in entities
> with the respective location id found in the second list:
>
> (def entities [{:name "foo" :location "us"} {:name "bar" :location "de"}])
> (def locations [{:location "us" :id 100} {:location "de" :id 101}])
>
> (reduce (fn [entities loc]
> (->> entities
> (map (fn [entity]
> (if (= (:location entity) (:location loc))
> (assoc entity :location (:id loc))
> entity)))))
> entities locations)
>
> => ({:name "foo", :location 100} {:name "bar", :location 101})
>
> This works, however it feels like there should be an easier way in clojure
> that is at minimum more readable, and ideally even more performant.
>
> Any suggestions?
>
> Thanks!
>
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