update nested map in clojure.

nested.clj

(def divisions
  {:division1
   {:group1 [:staff1 :staff2]
    :group2 [:staff3 :staff4 :staff5]}
   :division2
   {:group3 [:staff6 :staff7]}})

(reduce
 (fn [ds [d g staffs]]
   (assoc-in ds [d g] (remove #{:staff2} staffs)))
 divisions
 (for [[d groups] divisions
       [g staffs] groups]
   [d g staffs]))