[shootout] moment.scm

[Jens Axel Søgaard <jensaxel@soegaard.net>]

;; Moments.scm

(require (lib "list.ss"))  ; quiksort and mergesort

(define (main args)
  (let* ((sum 0.0)
  (numlist (let loop ((line (read-line)) (numlist '()))
      (cond ((eof-object? line) numlist)
     (else
      (let ((num (string->number line)))
        (set! sum (+ num sum))
        (loop (read-line) (cons num numlist))))))))
    (let ((n (length numlist)))
      (let ((mean (/ sum n))
     (average_deviation 0.0)
     (standard_deviation 0.0)
     (variance 0.0)
     (skew 0.0)
     (kurtosis 0.0)
     (median 0.0)
     (deviation 0.0))
 (let loop ((nums numlist))
      (if (not (null? nums))
   (begin
     (set! deviation (- (car nums) mean))
     (set! average_deviation (+ average_deviation (abs deviation)))
     (set! variance (+ variance (expt deviation 2.0)))
     (set! skew (+ skew (expt deviation 3.0)))
     (set! kurtosis (+ kurtosis (expt deviation 4)))
     (loop (cdr nums)))))

 (set! average_deviation (/ average_deviation (exact->inexact n)))
 (set! variance (/ variance (- n 1)))
 (set! standard_deviation (sqrt variance))

 (cond ((> variance 0.0)
        (set! skew (/ skew (* n variance standard_deviation)))
        (set! kurtosis (- (/ kurtosis (* n variance variance))
     3.0))))

 (set! numlist (quicksort numlist (lambda (x y) (< x y))))

 (let ((mid (quotient n 2)))
   (if (zero? (modulo n 2))
       (set! median (/ (+ (car (list-tail numlist mid))
     (car (list-tail numlist (- mid 1))))
         2.0))
     (set! median (car (list-tail numlist mid)))))


 (set! standard_deviation (/ (round (* standard_deviation 1000000))
1000000))

 (for-each display
                  `("n:                  " ,n                   "\n"
                    "median:             " ,median              "\n"
                    "mean:               " ,mean                "\n"
                    "average_deviation:  " ,average_deviation   "\n"
                    "standard_deviation: " ,standard_deviation  "\n"
                    "variance:           " ,variance            "\n"
                    "skew:               " ,skew                "\n"
                    "kurtosis:           " ,kurtosis            "\n" ))))))