Re: alter a map in a vector (reference)

[Kelker Ryan]

Here's the refactored version.

user> (def example
             (ref 
              [{:id 1 :email {"a...@mail.com" 1}}
               {:id 2 :email {"d...@mail.com" 1}}
               {:id 3 :email {"g...@mail.com" 2}}
               {:id 4 :email {"f...@mail.com" 2}}]))
#'user/example
user> 
(defn update-counter [id xs]
  (dosync
   (let [_ @xs
         at-after (drop-while #(not= id (:id %)) _)
         mod-key (-> at-after first :email keys first)
         location (- (count _) (count at-after))]
     (alter xs update-in [location :email mod-key] inc))))
#'user/update-counter
user> (dotimes [_ 3]
	     (update-counter 3 example))
nil
user> (clojure.pprint/pprint @example)
[{:email {"a...@mail.com" 1}, :id 1}
 {:email {"d...@mail.com" 1}, :id 2}
 {:email {"g...@mail.com" 5}, :id 3}
 {:email {"f...@mail.com" 2}, :id 4}]
nil

 

 

 

12.06.2013, 14:47, "Meikel Brandmeyer (kotarak)" <m...@kotka.de>:

Hi,

Am Mittwoch, 12. Juni 2013 06:39:59 UTC+2 schrieb Kelker Ryan:

user> (defn update-counter [id xs]

        (let [at-after (drop-while #(not= id (:id %)) @xs)
              to-modify (-> at-after first :email)
              mod-key (-> to-modify keys first)
              location (let [_ (- (count @xs) (count at-after))]
                         (if-not (pos? _) 0 _))]
          (dosync
           (alter xs update-in [location :email mod-key] inc))))

 

You have to wrap all accesses to xs in the same dosync.

 

Kind regards

Meikel

 

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