CSC 151.03, Class 33: Association lists

Overview

• Preliminaries
  • Notes and news
  • Upcoming work
  • Extra credit
  • Questions
  • Mentor evaluations
• Lab
• Debrief

News / Etc.

Upcoming Work

• No reading for Friday. Work on your projects.
• Writeup for class 32 due TODAY at 10:30 p.m.
  • Exercise 6
  • To: csc151-01-grader@grinnell.edu
  • Subject: CSC 151.01 Writeup 32 (YOUR NAMES)
• Writeup for class 33 due Friday at 10:30 p.m.
  • Exercises 4b and 4c. No documentation is required.
  • To: csc151-01-grader@grinnell.edu
  • Subject: CSC 151.01 Writeup 33 (YOUR NAMES)
• Exam 3 cover pages due NOW!
  • Did you put your number on the sheet?
  • Did you sign both statements (if you feel comfortable doing so)?
  • Did you date both statements?
  • Did you remove the ra-cha-fringies if you removed the paper from a notebook?
• Exam 3 Epilogues due TONIGHT!
  • One of the best comments so far: “This would have been much easier if I did the self-check problems every day.”
• Quiz Friday!
  • Association lists, algorithm efficiency, maybe trees
  • Mentor sessions tonight at 8pm, tomrrow at 7pm and 8pm.

Extra credit (Academic/Artistic)

• Pub-free quiz at Bob’s. TONIGHT 9pm (I think). Stats-Math focus.
• Convocation Thursday at 11 a.m. in JRC 101. “Work’s Provocative Future: Which Graduates Will Thrive?”
• Social Media in the U.S. and China, Thursday, Nov. 16, 7-9pm JRC 2nd. Chinese snacks provided.

Extra credit (Peer)

• “The First Time I Walked on the Moon”. Four, count ‘em, four performances. Thursday at 7:30, Friday at 7:30, Saturday at 7:30, Sunday at 2:00.
  • “You’ve got to pay attention to what’s going on.”
• Orchestra, Saturday at 2pm

Extra credit (Misc)

Other good things

• Fresh Flutes Thursday
• Voice recitals Friday at 4:15 (Henderson) and 7:00 (Manuel)
• Women’s Basketball vs. Emmaus TONIGHT at 5:00 p.m.
• Men’s Basketball vs. Emmaus TONIGHT at 7:00 p.m.
• Swimming and Diving Saturday at 1:00 p.m.

Questions

When should I turn a list into a vector?

If, for example, you don’t expect to change the length and you are doing a lot of calls to list-ref.

What did that mean?

I have a list, like ‘(“Scooby Doo” “Shaggy” “Velma” “Fred” “Daphne” “Scrappy Doo” “The Van”)

If it seems like I’m doing things like (list-ref best-show-ever 4) I’m probably better off turning it into a vector. vector-ref is much faster than list-ref.

If it seems like characters are being added, (cons "Another Zombie" best-show-every)`, I don’t want a vector.

Best show ever, really?

No.

How does the vector procedure turn its elements into a vector?

Magic.

Explain: “Some of you may recall that we said that “if can take a value other than #t or #f. Here’s an example why.”

The nearby code looks something like the following.

(let ([result (assoc "Scooby" tv-shows)])
  (if result
      (cadr result)
      #f))

When would you want to turn a vector into a list?

Most frequently, when you want to use one of the handy-dandy list procedures we have already, like filter.

Can I redefine a variable within a procedure?

Yes, but that practice is usually discouraged because it may confuse the reader

(define my-proc
  (lambda (val)
    (let ([+ -])
      (+ val 2))))

Mentor and tutor evaluations

• Goal: Improve our program

Lab

Writeup is 4b and 4c.

Can we make up the cartoon characters and sidekicks?

Sure.

("Zandy Proton" "Sky Rebel")

("UM, the Ulimate Mentor" "UH, the Ultimate Helper")

What should multi-assoc return in the base case?

“multi-assoc returns a list of matching entries”

So it should return a list.

What list is appropriate?

Do you have hints for writing multi-assoc?

Don’t call assoc.

Look at the pattern we have for recursing over a list. (Or how assoc is defined.)

Debrief