schema.clj

(ns schema
  (:use clojure.test))

(defn apply-schema [schema data]
  (if (vector? data)
    (vec (map #(apply-schema (first schema) %) data))
    (reduce merge (map (fn [item] (if (keyword? item)
                                     {item (data item)}                                
                                     (let [[[k v]] (vec item)]
                                       {k (apply-schema v (data k))})))
                  schema))))

(with-test
    (def test-data {
        :aaa "22"
        :aaaa "New 22"
        :bbb "434"
        :ccc {:ddd "abc" :ddddd "Not needed" :ggg "Needed" :hard_to_believe []}
        :zzz [ {:hhh  126 :hhhh "Don't need" :kkk  "Existing key"} {:hhh  "DoobyDo" :kkk  "Needed" :mmm  "Existing key"} ]})
 
    (def test-schema [
        :aaa
        :bbb
        :ooo
        {:ccc [:ddd :ggg]}
        {:zzz [[:hhh :kkk :mmm]]}])
    (is (= (apply-schema test-schema test-data)          
      { :zzz [{:mmm nil, :kkk "Existing key", :hhh 126} {:mmm "Existing key", :kkk "Needed", :hhh "DoobyDo"}]
        :ccc {:ggg "Needed", :ddd "abc"}
        :ooo nil
        :bbb "434"
        :aaa "22"}))
        )