How do I add an element to an array-map in Clojure?

Question

How can I add an element to an array-map in Clojure? I tried using assoc but it doesn\'t get added? I essentially want to set a default value of 0 for any missing items in the e

Answer 1

To supplement Carcigenicate's answer, another suggestion: I'd use merge or assoc on a map of defaults:

(merge {:default-1 123 :default-2 234} {:default-1 "foo"})
=> {:default-1 "foo", :default-2 234}

Note that the order of arguments to merge matters i.e. right-most maps take precedence over left-most maps. Your default map values will only "survive" if they're not overridden by additional map(s).

(def defaults {"foo" 0, "bar" 0})
(defn create-entry [doc]
  (assoc defaults "id" (str (java.util.UUID/randomUUID))))
(defn create-entry [doc]
  (merge defaults {"id" (str (java.util.UUID/randomUUID))}))

Using assoc in this example has the same effect, and I'd prefer that version.