Discovery how require a file in Clojure and group a list of maps by keyword

#clojure #todayilearned

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We have into our namespace example a .clj with demands, we need to import it in another .clj for handle the demands, like groupping by a keyword for example.

In clojure we define a namespace by `(ns my-namespace)`

db.clj:

(ns example.db)  

(def demand {:user 15  
  :itens {:bag {:id :bag :quantity 3 :price 80}  
                     :t-shirt {:id :t-shirt :quantity 3 :price 40}  
                     :shoes {:id :shoes :quantity 3}}})  
(def demand2 {:user 15  
  :itens {:bag {:id :bag :quantity 3 :price 80}  
                     :t-shirt {:id :t-shirt :quantity 3 :price 40}  
                     :shoes {:id :shoes :quantity 3}}})  
(def demand3 {:user 15  
  :itens {:bag {:id :bag :quantity 3 :price 80}  
                     :t-shirt {:id :t-shirt :quantity 3 :price 40}  
                     :shoes {:id :shoes :quantity 3}}})  
(def demand4 {:user 11  
  :itens {:bag {:id :bag :quantity 2 :price 80}  
                     :t-shirt {:id :t-shirt :quantity 3 :price 40}  
                     :shoes {:id :shoes :quantity 7}}})  

(def demand5 {:user 11  
  :itens {:bag {:id :bag :quantity 5 :price 80}  
                      :t-shirt {:id :t-shirt :quantity 3 :price 40}  
                      :shoes {:id :shoes :quantity 30}}})  

(defn all-demands []  
  [demand, demand2, demand3, demand4, demand5])

handle.clj:

For import another file, just pass in your local namespace the keyword :require to import for the standard definition namespace.file-name, and if you want you can add an alias using :as keyword, good pratices encourages us to follow same standard but abbreviated

(ns example.handle  
  :require '[example.db :as e.db]) 
(println (group-by :user (l.db/all-demands))) ;group all demands by user

;if you want count total per user you can do something like that:
(defn total-per-user [[user demands]]  
  {:user-id user  
   :total (count demands)})  

(->> (l.db/all-demands)  
     (group-by :user)  
     (map total-per-user)  
     println)