(define (entropy input)
  (define (close? a b)
    (define (norm x y)
      (define (infinite_norm m n)
        (define (absminus p q)
             (cond ((null? p) '())
                (else (cons (abs (- (car p) (car q))) (absminus (cdr p) (cdr q))))))
        (define (mm l)
             (cond ((null? (cdr l)) (car l))
                   ((> (car l) (cadr l)) (mm (cons (car l) (cddr l))))
                   (else (mm (cdr l)))))
        (mm (absminus m n)))
      (if (pair? x) (infinite_norm x y) (abs (- x y))))
    (let ((epsilon 0.2))
      (< (norm a b) epsilon)))
  (define (freq-list x)
    (define (f x)
      (define (count a b)
        (cond ((null? b) 1)
              (else (+ (if (close? a (car b)) 1 0) (count a (cdr b))))))
      (let ((t (car x)) (tt (cdr x)))
        (count t tt)))
    (define (g x)
      (define (filter a b)
        (cond ((null? b) '())
              ((close? a (car b)) (filter a (cdr b)))
              (else (cons (car b) (filter a (cdr b))))))
      (let ((t (car x)) (tt (cdr x)))
        (filter t tt)))
    (cond ((null? x) '())
          (else (cons (f x) (freq-list (g x))))))
  (define (scale x)
    (define (sum x)
      (if (null? x) 0.0 (+ (car x) (sum (cdr x)))))
    (let ((z (sum x)))
      (map (lambda(m) (/ m z)) x)))
  (define (cal x)
    (if (null? x) 0 (+ (* (car x) (/ (log (car x)) (log 2))) (cal (cdr x)))))
  (- (cal (scale (freq-list input)))))

(entropy (list 1 2 2 3 3 3 4 4 4 4))
(entropy (list (list 1 1) (list 1.1 1.1) (list 1.2 1.2) (list 1.3 1.3) (list 1.5 1.5) (list 1.6 1.6)))