Parse a CSV file containing rows like "2008,08,1.8,45454,8900,coupe" into a map that looks like: { "2008/1.8/coupe" [ {:mileage 45454 :price 8900}, ... ] ... } that can be further used to extract summary stats.

gistfile1.clj

(defn group-car-data-by-model [in-file]
  (with-open [in-file (io/reader in-file)]
    (loop [results {}
           rows (doall (csv/read-csv in-file))]
      (if (empty? rows)
        results
        (let [[year reg engine mileage price kind] (first rows)
              model (str year "/" engine "/" kind)
              cars (get-in results [model] [])]
          (recur (assoc-in results [model] (conj cars {:mileage mileage
                                                       :price price}))
                 (rest rows)))))))

(println (group-car-data-by-model (project-path "mx5.csv")))