Live coding session at Lisp Meet Up #11. Make a frequency table and a histogram for a given list of floating point numbers.

meetup11.lisp

;;; Utility
(defun iota (num &key (start 0) (step 1))
  (do ((i start (+ i step))
       (acc '() (cons i acc))
       (c 0 (1+ c)))
    ((= c num) (nreverse acc))))

(defparameter *floats*
  (mapcar (lambda (x)
            (declare (ignore x))
            (float (/ (random 1000) 1000)))
        (iota 1000)))

(let ((interval 0.05)
      (table (make-hash-table)))
  (dolist (elem *floats*)
    (incf (gethash (floor elem interval) table 0)))
  (let ((lst ()))
    (maphash (lambda (k v)
               (push (list (* k interval) (map 'string (constantly #\*) (iota v))) lst))
             table)
    (format t "~{~&~{~6,2F : ~A~}~}"
    (sort lst #'< :key #'car))))

;;; Another implementation
(let ((interval 0.05)
      (table (make-hash-table)))
  (dolist (elem *floats*)
    (incf (gethash (floor elem interval) table 0)))
  (let ((lst ()))
    (maphash (lambda (k v)
               (push (list (* k interval) (make-list v :initial-element #\*)) lst))
             table)
    (format t "~{~&~{~6,2F : ~{~A~}~}~}"
    (sort lst #'< :key #'car))))

;;; Yet another one
(let ((interval 0.05)
      (table (make-hash-table)))
  (dolist (elem *floats*)
    (incf (gethash (floor elem interval) table 0)))
  (let ((lst ()))
    (maphash (lambda (k v)
               (push (list (* k interval) (iota v)) lst))
             table)
    (format t "~{~&~{~6,2F : ~{*~*~}~}~}"
    (sort lst #'< :key #'car))))

(make-string v :initial-element #\*)なんて方法もあるみたいです

気が付きませんでしたが、そのやり方が簡潔ですね。