Obtain diff between source data and golden view

source-gold-diff.clj

(def api-data {:source-data {:fname "Ray", :last "McDermott", :e-mail "[email protected]"},
               :golden-view {:first "Ray", :last "McDermott", :email "[email protected]", :dob "29/04/2004"},
               :mapping {:email :e-mail, :first :fname, :last :last}})
;=> #'user/api-data

(defn source-golden-diff [source-data golden-view source-map]
  (let [common-keys (let [keys (clojure.set/intersection (set (keys golden-view))
                                                         (set (keys source-data)))]
                      (into {} (map #(vec [% %]) keys)))

        all-keys (merge common-keys source-map)

        diffs (let [golden-view-of-source (into {} (map #(assoc {} (first %) (get source-data (last %))) all-keys))]
                (into {} (clojure.set/difference (set golden-view-of-source) (set golden-view))))]

    (into [] (map (fn [diff-key] (let [src-key (get all-keys diff-key)
                                       new-src-value (get golden-view diff-key)
                                       old-src-value (get source-data src-key)]
                                   {:new    [src-key new-src-value]
                                    :old    [src-key old-src-value]
                                    :golden [diff-key new-src-value]})) (keys diffs)))))
;=> #'user/source-golden-diff

(source-golden-diff (:source-data api-data) (:golden-view api-data) (:mapping api-data))
;=> {:new [:e-mail "[email protected]"], :old [:e-mail "[email protected]"], :golden [:email "[email protected]"]}

The mapping is the non-matching elements that map between the source and golden view.
In this case the source system does not hold DOB. The :last field is common.
Small fix to use all-keys in the final form.