Laboratory: Ruby (3)

Summary:

Prerequisites: The first Ruby lab. The second Ruby lab. Tate, Chapter 2

Contents:

• Preparation
• Exercises
  • Exercise 1: CSV Basics
  • Exercise 2: A Constructor
  • Exercise 3: Columns
  • Exercise 4: Columns, Revisited
• For Those Extra With Extra Time
  • Extra 1: Rows
  • Extra 2: Iteration

Preparation

a. Create a directory for this lab. I would recommend something like csc302/ruby/lab3, but it's up to you.

b. Start the interactive ruby interpreter with irb.

c. In your browser, you may want to open a link to the code from Tate.

Exercises

Exercise 1: CSV Basics

a. Pick the simplest implementation of the CSV wrapper and verify that it works as advertised.

b. Determine what happens if the rows are shorter than or longer than the number of headers.

Exercise 2: A Constructor

Right now, ActsAsCsv ties the name of the class to the name of the file. Write a constructor that accepts an optional filename.

Exercise 3: Columns

Add a method to the ActsAsCsv class called column that takes one parameter, the name of a column, and returns an array of all the values in that column.

Exercise 4: Columns, Revisited

Using the method_missing hack, support procedures for each of the column names. E.g., if the CSV file has a column named grade, it should be possible to call csv.grade and get that column.

You should use raise "No such method" (or something similar) if an invalid column name is given.

For Those Extra With Extra Time

Extra 1: Rows

Create another class, CsvRow, that represents one row in a CSV file. The class should permit you to extract a value in a row by column number or by name. (Call the methods whatever you'd like.)

Extend your ActsAsCsv class with a method that returns rows by number.

Extra 2: Iteration

Implement an each method for ActsAsCsv that calls its parameter on a each CsvRow.