Prints a horizontal ASCII bar chart for the data given. Written in Clojure.

ascii-bar-chart.clj

(defn ascii-bar-chart
  "
  Prints the horizontal ASCII bar chart for the data given.
  Handles both positive and negative values.
  Use it to visualize data in the REPL.
   
  Arguments:
    data: a seq of key value pairs. the chart is printed in the order of this seq.
      keys should be strings (or have a proper toString method).
      values should be numbers.
    marker: the string to use as the marker in the chart.
    scale: the scale of the chart.
    
  Example:
    user=> (ascii-bar-chart [[\"Jan\" 80] [\"Feb\" -50] [\"Mar\" 35] [\"Apr\" -10]] \"|\" 40)
                    |||||||||||||||||||||||||| Jan - 80
     ||||||||||||||||                          Feb - -50
                    ||||||||||||               Mar - 35
                 ||||                          Apr - -10
    nil
  "
  [data marker scale]
  (let [vals (map second data)
        max-val (apply max vals)
        min-val (apply min vals)
        val-range (- (max 0 max-val) (min 0 min-val))
        scaled-min-val (/ (* scale (- min-val)) val-range)
        scaled-max-val (/ (* scale max-val) val-range)
        marker-len (count marker)]
    (doseq [[k v] data]
      (let [neg-bars (if (< v 0) (round (/ (* scale (- v)) val-range)) 0)
            pos-bars (if (>= v 0) (round (/ (* scale v) val-range)) 0)
            neg-ws (- scaled-min-val neg-bars)
            pos-ws (- scaled-max-val pos-bars)]
      (println
        (str
          (apply str (take (* marker-len neg-ws) (repeat " ")))
          (apply str (take neg-bars (repeat marker)))
          (apply str (take (inc pos-bars) (repeat marker)))
          (apply str (take (* marker-len pos-ws) (repeat " "))))
        k "-" v)))))