You’re right, I missed a step :-). Something like (typed in-line so it really
won’t compile):
:locations [{“us” 100} {“de” 101}]
:locations-seq (into {} (map (fn [{:keys [location]}] [:location (get locations
location)])…)
;; the above produces a sequence symmetrical with entities, each map containing
{:location id} where id is the correct ID for the matched entity).
(map #(apply merge) entities locations-seq)
Your solution is nicer and more efficient and doesn’t rely on ordering either.
That will teach me for multi-tasking :-).
> On 13 Sep 2015, at 5:09 PM, Brian Platz <bpl...@gmail.com> wrote:
>
> 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
>> <http://gmail.com/>> 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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