gistfile1.clj

[{: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}]}]

;; becomes

[{:metric1
  [{:date1 [{"user 1" 1}
            {"user 2" 3}]}
   {:date2 [{"user 1" 5}
            {"user 2" 7}]}]}
 {:metric2
  [{:date1 [{"user 1" 2}
            {"user 2" 4}]}
   {:date2 [{"user 1" 6}
            {"user 2" 8}]}]}]