gistfile1.clj

(let [inputs [{:date1
              [{:user "user 1"
                :metric1 1
                :metric2 2}
               {:user "user 2"
                :metric1 3
                :metric2 4}]}
             {:date2
              [{:user "user 1"
                :metric1 5
                :metric2 6}
               {:user "user 2"
                :metric1 7
                :metric2 8}]}]]
  (reduce (fn [m path]
            (assoc-in m (pop path) (peek path)))
          {}
          (for [input inputs,
                [date objs] input
                obj objs
                :let [user (:user obj), obj (dissoc obj :user)]
                [metric value] obj]
            [metric date (str "user " user) value])))