(defstruct dist 
  (min    most-positive-double-float) 
  (max    most-negative-double-float) 
  (bars   '()) 
  (sum    0)
  (sumsq  0)
  (n      0)
  (sorted t)
  (fuzz   1)
  (fat   nil)
  (all    '())
)

(defun dist-compare (d1 d2 &key (conf 95))
  "compares means of two independent samples d1 d2"
  (ttest (dist-sum d1) (dist-sumsq d1) (dust-n d1)
	 (dist-sum d2) (dist-sumsq d2) (dust-n d2)
	 :conf conf))

(defun as-dist (l)
  "Return a dist with all the numbers of l"
  (if (eq 'dist (type-of l))
      l
      (dist-adds l)))

(defun dist-adds (l &optional (d (make-dist)))
  "Add the numbers in the list 'l' to a dist."
  (dolist (x l d)
    (dist-add x d)))

(defun dist-mean (d)
  (/ (dist-sum d) (dist-n d)))

(defun dist-sd (d)
  (stdev (dist-n d) (dist-sum d) (dist-sumsq d)))

(defun dist-add (num &optional (d (make-dist)))
  (incf (dist-n      d))
  (incf (dist-sum    d) num)
  (incf (dist-sumsq  d) (* num num))
  (if (dist-fat d) (push num (dist-all d)))
  (if (< num (dist-min d)) (setf (dist-min d) num))
  (if (> num (dist-max d)) (setf (dist-max d) num))
  (let* ((fuzz (dist-fuzz d))
	 (num1 (* fuzz (round (/ num fuzz))))
	 (val  (cdr (assoc num1 (dist-bars d)))))
    (if val
	(setf (cdr (assoc num1 (dist-bars d))) (1+ val))
	(push (cons num1 1) (dist-bars d)))
    (setf (dist-sorted d) nil))
  d)

(defun dist-sort (d)
  (labels ((car< (a b) (< (car a ) (car b))))
    (unless (dist-sorted d) 
      (setf (dist-bars d) (sort (dist-bars d) #'car<)
	    (dist-sorted d) t))
    d))