Nested DEF

pick-and-rename.clj

(defn pick-and-rename [col pick-map]
  (def undefined-value (atom :undefined-value))
  (apply assoc
         {}
         (flatten
          (filter (fn [[k v]]
                    (not (= v undefined-value)))
           (map (fn [[k v]]
                  [v (get col k undefined-value)])
                pick-map)))))