solved with clojure.core

gistfile1.clj

(->> [{:name "jay fields", :current-city "new york", :employer "drw.com"}
      {:name "john dydo", :current-city "new york", :employer "drw.com"}
      {:name "mike ward", :current-city "chicago", :employer "drw.com"}
      {:name "chris george", :current-city "new york", :employer "thoughtworks.com"}]
     (map (juxt :employer (comp list :name)))
     (map (partial apply hash-map))
     (apply merge-with concat))