group-by

(define (group lst n)
  (define (group2 n2 lst2 group grouped)
    (define (join lst1 lst2)
      (append lst1 (list (reverse lst2))))
    (cond ((empty? lst2) (join grouped group))
          ((= n2 0) (group2 n lst2 '() (join grouped group)))
          (else (group2 (- n2 1) (mcdr lst2) (cons (car lst2) group) grouped))))
   (group2 n lst '() '() ))