make an text histogram from a vector of integers

histog.clj

;; From the REPL
(require '[clojure.math.numeric.tower :as math])

(defn histo
  [v & {:keys [size] :or {size 40}}]
  (letfn [(digits-for-num [x]
            (inc
              (int (math/floor (/ (Math/log x) (Math/log 10))))))]
    (let [mm (apply max v)
          digits-x (digits-for-num (count v))
          digits-y (digits-for-num mm)
          frmt-spec-x (str "%0" digits-x "d")
          frmt-spec-y (str "%0" digits-y "d")
          f (/ (float size) mm)]
      (map-indexed  
           (fn [i e]
             (let [ne (Math/round (* f e))
                   x-l (format frmt-spec-x i)
                   y-l (format frmt-spec-y e)
                   stars (apply str (repeat ne "*"))]
               (str x-l ":" stars "(" y-l ")")))
           v))))