There is clojure.set/join to do exactly what you are asking for:
```
(-> (clojure.set/join entities locations)
(clojure.set/rename {:id :location}))
;=> ({:name "bar", :location 101} {:name "foo", :location 100})
```
(I'm also using clojure.set/rename to rename :id to :location)
http://clojuredocs.org/clojure.set/join
(join xrel yrel)
(join xrel yrel km)
When passed 2 rels, returns the rel corresponding to the natural
join. When passed an additional keymap, joins on the corresponding
keys.
On Sun, Sep 13, 2015 at 11:14 AM, Brian Platz <bpl...@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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