Exercise #9

The file /home/stone/courses/scheme/examples/population-data.ss contains a body of information about the ninety-nine counties of the state of Iowa: their names, their populations in 1990 and in 2002, and their areas (in square miles). The information is presented in the form of a Scheme definition that constructs and names a vector in which each element is a record giving these four facts about counties:

(define population-data
  (vector
    (make-county "Adair" 8331 7987 570)
    (make-county "Adams" 4553 4384 426)
    (make-county "Allamakee" 13941 14591 660)
        ...
    (make-county "Woodbury" 101187 103331 877)
    (make-county "Worth" 7874 7766 402)
    (make-county "Wright" 14201 13986 582)))

This definition presupposes that there is a make-county procedure that constructs and returns such records. The first part of the exercise, therefore, is to design and implement the primitive procedures for county records, including the constructor make-county.

With these procedures, program the computer to answer some questions about Iowa demographics:

• Determine how many Iowa counties lost population from 1990 to 2002.
• Construct a list of the counties of Iowa, sorted into decreasing order by population density (number of inhabitants per square mile).
• Print out a list of the counties of Iowa, sorted by percentage population gain or loss from 1990 to 2002, printing the counties that gained population most rapidly (as a percentage of their 1990 populations) first and the counties that lost population most rapidly last. For each county, print out both its name and its percentage population gain or loss.

This exercise will be due at 9 a.m. on Wednesday, April 28.

This document is available on the World Wide Web as

http://www.cs.grinnell.edu/~stone/courses/scheme/exercises/9.xhtml

created April 21, 2004
last revised April 23, 2004

John David Stone (stone@cs.grinnell.edu)