1. David Evans http://www.cs.virginia.edu/evans
Lecture 11: Sorting Grounds and Bubbles
Coffee Bean Sorting in Guatemala
CS200: Computer Science
University of Virginia
Computer Science
David Evans

2. Menu
Find Most
Sorting
10 February 2003
CS 200 Spring 2003

3. find-most-caffeinated
(define (find-most-caffienated menu)
(insertl
(lambda (c1 c2)
(if (> (coffee-caffeine-rating c1)
(coffee-caffeine-rating c2))
c1 c2))
menu
(make-coffee “water” )))
;; we should only water if there are no coffees
;; on the menu
10 February 2003
CS 200 Spring 2003

4. find-most-caffeinated
(define (find-most-caff menu)
(if (null? menu)
(make-coffee “water" )
(let ((rest-most-caff
(find-most-caff (cdr menu))))
(if (> (coffee-caffeine-rating (car menu))
(coffee-caffeine-rating rest-most caff))
(car menu)
rest-most-caff))))
10 February 2003
CS 200 Spring 2003

5. Comparing Processes > (trace >) (>)
> (find-most-caff todays-menu)
|(> 57 -1)
|#t
|(> 15 57)
|#f
|(> 12 57)
|(> 92 57)
|(> 85 92)
("BEN'S Expresso Noir Supreme" )
> (find-most-caffienated todays-menu)
|(> 57 -1)
|#t
|(> 15 57)
|#f
|(> 12 57)
|(> 92 57)
|(> 85 92)
("BEN'S Expresso Noir Supreme" )
10 February 2003
CS 200 Spring 2003

6. Sorting
10 February 2003
CS 200 Spring 2003

7. Simple Sorting We know how to find-most-caffeinated
How do we sort list by caffeine rating?
Use (find-most-caffeinated menu) to find the most caffeinated
Remove it from the menu
Repeat until the menu is empty
10 February 2003
CS 200 Spring 2003

8. Delete ;;; Evaluates to the list parameter with
;;; first instance of el removed.
(define (delete lst el)
(if (null? lst)
(error "Element not found!")
(if (eq? (car lst) el)
(cdr lst)
(cons (car lst)
(delete (cdr lst) el)))))
10 February 2003
CS 200 Spring 2003

9. sort-menu (define (sort-menu menu) (if (null? menu) menu
(let ((most-caff
(find-most-caffeinated menu)))
(cons
most-caff
(sort-menu
(delete menu most-caff))))))
How can we generalize this? (e.g., sort by price also)
10 February 2003
CS 200 Spring 2003

10. All Sorts (define (sort cf lst) (if (null? lst) lst
(let ((most (find-most cf lst)))
(cons
most
(sort cf
(delete lst most))))))
10 February 2003
CS 200 Spring 2003

11. Caffeine Sorts (define (sort-menu-by-caffeine menu)
(sort (lambda (c1 c2)
(> (coffee-caffeine-rating c1)
(coffee-caffeine-rating c2)))
menu))
10 February 2003
CS 200 Spring 2003

12. find-most (define (find-most cf lst) (insertl (lambda (c1 c2)
(if (cf c1 c2) c1 c2))
lst
(car lst)))
10 February 2003
CS 200 Spring 2003

13. Charge PS3 Due Wednesday
Lab Hours: Tonight, 6-7:30 PM in Small Hall
Think about faster ways of sorting (next time)
Read Tyson’s essay (before Friday)
How does it relate to  (n2)
How does it relate to grade inflation
10 February 2003
CS 200 Spring 2003