Why Not a Function #3: dissoc-in

(defn dissoc-in
  [m [k & knext :as ks]]
  (cond
    (and knext
      (contains?
        (get-in m (butlast ks))
        (last ks))) (update-in m (butlast ks) dissoc (last ks))
    (not knext) (dissoc m k)
    :else m))

dissoc-in is a mixture of assoc-in and dissoc. It lets us remove an entry from a nested associative structure using a path of keys.

(assoc-in {:pencil "blue"} [:computer :mouse :left-button] "green")
=> {:pencil "blue", :computer {:mouse {:left-button "green"}}}

(dissoc-in *1 [:computer :mouse :left-button])
=> {:pencil "blue", :computer {:mouse {}}}

It doesn’t make any changes if the key path does not exist.

(dissoc-in *1 [:monitor :stand])
=> {:pencil "blue", :computer {:mouse {}}}

Written on March 12, 2020