appsbytable.clj

(ns meetup)

(def myinput { :app1 #{:t1 :t2}  :app2 #{:t2 :t3} :app3 #{:t2 :t3 :t4}})

(defn update-table [outputmap table app]
  (assoc outputmap table (conj (or (outputmap table) #{}) app)))

(defn process-tables [outputmap [app tables]]
  (loop [map outputmap appname app ts tables]
    (if (empty? ts)
      map
      (recur (update-table map (first ts) app) app (rest ts)))))

(defn process-apps [app-hash]
  (loop [items (seq app-hash) output {}]
    (if (empty? items)
      output
      (recur (rest items) (process-tables output (first items))))))