--- title: Eboard 30 Analyzing procedures number: 30 section: eboards held: 2017-11-08 --- CSC 151.01, Class 30: Analyzing procedures =========================================== _Overview_ * Preliminaries * Notes and news * Upcoming work * Extra credit * Questions * Debrief on yesterday's lab. * Quick review of homework 6. * Lab. * Debrief. ### News / Etc. * Quiz 9 returned. * If you take notes on the gridded cards, please discard your notes when you leave. * We will probably not get through more than half of today's lab today. That's okay. There's lab time on Friday. * It's preregistration time. Things to consider: * CSC 161 is an awesome course. I'm told it's very different than 151. (For some, that's a positive. For others, that's a negative.) * Wilson short course: Human Centered Design for Global Social Transformation * Wilson short course: Leadership in a Future of Automation and Income Inequality. * ENG 295-01. Lighting the Page: Digital Methods in Literary Studies. (ENG-120 prereq) * HIS 295-01. Digital Methods in Historical Studies. (HIS-100 prereq) ### Upcoming Work * [Writeup for class 29](../writeups/writeup29) due Wednesday at 10:30 p.m. * Exercise 6, no documentation necessary. * To: * Subject: CSC 151.01 Writeup 29 (YOUR NAMES) * Read [Project description](../assignments/project) for Friday's class. * No, it's not ready. * [Exam 3](../exams/exam03) * Prologue due Friday. * Exam due Tuesday the 14th. * Cover pages due Wednesday the 15th. * Epilogues due Wednesday the 15th. * Quiz Friday * Trees * Higher-order procedures * Files ### Extra credit (Academic/Artistic) * Crip Technoscience, Disabled People as Makers and Knowers, Wednesday, Nov. 8, 4:15 p.m., JRC 101. * Workshop by Sanjay Khanna '85 "Khanna can pitch. Can you?" Tonight at 7pm in ARH 120. Sign up at ### Extra credit (Peer) * Voice Recital (students of Nicolas Miguel), Friday, 7ish, Sebring-Lewis ### Extra credit (Misc) * Pioneer weekend. (Today is the last day to sign up.) ### Other good things * Pub Quiz tonight! (At Bobs) * Anime talk tomorrow night. ### Questions #### On the exam Can I use `length` on problem 1? : I'd prefer that you didn't. : Snarky answer: Sure, if you don't care about getting full credit. I have questions about a particular strategy I'm using. Can I reveal it to the whole class or should I email you? : Email me. #### On the analysis reading #### On other topics How do I write a procedure that turns a pair structure into a string? ``` (define pair-structure->string (lambda (val) (cond [(integer? val) (number->string val)] [(null? val) "()"] [(pair? val) (string-append "(" (pair-structure->string (car val)) ; Goal of kernel: Produce the string for everything that's left/ (let kernel ([remaining (cdr val)]) (cond [(number? remaining) (string-append " . " (number->string remaining))] [(null? remaining) ""] [(pair? remaining) (string-append " " (pair-structure->string (car remaining)) (kernel (cdr remaining)))] [else " still-not-sure"])) ")")] [else "I'm not ready to handle that yet"]))) ``` Debrief from prior class ------------------------ ### How did you figure out that the sum was correct? * `(apply + (map string->number (file->words FILE)))` * Open the file in DrRacket. Put `(+` at the start. Put ')' at the end. Evaluate. * Open the file in a spreadsheet and use the spreadsheet sum. Notes on HW6 ------------ Problem 1: Partitition * Key idea: If you are partition a list of n elements into k pieces, Make a piece of size n/k and then recurse. * Partition takes as input a list and a positive integer and returns a list of lists. * Starting point: `(if (= 1 k) (list lst) ...)` * Why `(list lst)` and not `lst`? Because I know that my return type is "list of lists". Code ``` #lang racket (require csc151) ; partition lst into k mostly-equal size pieces (define partition1 (lambda (lst k) (if (= 1 k) (list lst) ; Three things ; Grab the first length/k elements ; recurse on the remaining elements ; Join 'em together (cons (take lst (ceiling (/ (length lst) k))) (partition1 (drop lst (ceiling (/ (length lst) k))) (- k 1)))))) (define partition2 (lambda (lst k) (if (= 1 k) (list lst) ; Three things ; Grab the first length/k elements ; recurse on the remaining elements ; Join 'em together (let ([num-elements-in-first-list (ceiling (/ (length lst) k))]) (cons (take lst num-elements-in-first-list) (partition2 (drop lst num-elements-in-first-list) (- k 1))))))) (define partition (lambda (lst k) (let kernel ([lst lst] [k k] [len (length lst)]) (if (= 1 k) (list lst) ; Three things ; Grab the first length/k elements ; recurse on the remaining elements ; Join 'em together (let ([num-elements-in-first-list (ceiling (/ len k))]) (cons (take lst num-elements-in-first-list) (kernel (drop lst num-elements-in-first-list) (- k 1) (- len num-elements-in-first-list)))))))) ; Determine if a string is a palindrome. ; Goal: Use numeric recursion. (define palindrome? (lambda (str) (let kernel ([left 0] [right (- (string-length str) 1)]) (if (>= left right) #t (and (char=? (string-ref str left) (string-ref str right)) (kernel (increment left) (decrement right))))))) (define remove-at (lambda (lst pos) (if (zero? pos) (cdr lst) (cons (car lst) (remove-at (cdr lst) (decrement pos)))))) (define insert-at (lambda (lst val pos) (if (zero? pos) (cons val lst) (cons (car lst) (insert-at (cdr lst) val (decrement pos)))))) (define insert-everywhere (lambda (val lst) (let ([len (length lst)]) (let kernel ([pos 0]) (if (> pos len) null (cons (insert-at lst val pos) (kernel (+ pos 1)))))))) (define perms (lambda (lst) ; Base case: Singleton or empty list (if (or (null? lst) (null? (cdr lst))) (list lst) (let ([partial (perms (cdr lst))] ; A list of permutations of part of the list [first (car lst)]) ; Sam's goal: Insert first into each element of partial. ; Then join 'em together (let kernel ([remaining partial]) (if (null? remaining) null (append (insert-everywhere first (car remaining)) (kernel (cdr remaining))))))))) ``` Lab --- Debrief -------