Trying to figure out why Ruby is throwing error on some basic classes & methods

Question

I have written some code out of the Ruby Pickaxe book and I am trying to get it to work. (around page 62 of "Programming Ruby The Pragmatic Programmer's Guide") **Edit: More info on the book: (C) 2009, for Ruby 1.9

Given this error message, I am not quite sure how to identify what is going wrong. I appreciate any help in understanding what is going wrong here.

How does one know what to identify and solve? I am wondering if Ruby's CSV functionality is really just this easy-- no gem/bundle install to run?

I would really like to be able to run my test_code.rb file, but I am unable to figure out this error.

Thank you for your time, Patrick

---

Note: all of these files are in the same directory.

IRB command, followed by the error message it generates:

2.1.1 :005 > load "test_code.rb"
LoadError: cannot load such file -- csv-reader
    from /Users/patrickmeaney/.rvm/rubies/ruby-2.1.1/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
    from /Users/patrickmeaney/.rvm/rubies/ruby-2.1.1/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
    from test_code.rb:3:in `<top (required)>'
    from (irb):5:in `load'
    from (irb):5
    from /Users/patrickmeaney/.rvm/rubies/ruby-2.1.1/bin/irb:11:in `<main>'

---

I don't know how relevant this is, based on the error message, but thought I'd include it. kernel_require.rb line 55:

if Gem::Specification.unresolved_deps.empty? then
  begin
    RUBYGEMS_ACTIVATION_MONITOR.exit
    return gem_original_require(path)
  ensure
    RUBYGEMS_ACTIVATION_MONITOR.enter
  end
end

line 9-11 of irb:

require "irb"

IRB.start(__FILE__)

---

First file of program: csv-reader.rb

require 'csv'
require 'book-in-stock'

class CsvReader

  def initialize
    @books_in_stock = []
  end

  def read_in_csv_data(csv_file_name)
    CSV.foreach(csv_file_name, headers: true) do |row|
      @books_in_stock << BookInStock.new(row["ISBN"], row["Amount"])
    end
  end

  def total_value_in_stock
    sum = 0.0
    @books_in_stock.each {|book| sum += book.price}
  end

  def number_of_each_isbn
  end

end

---

Second file: book-in-stock.rb

class BookInStock
  attr_reader :isbn
  attr_accessor :price

  def initialize(isbn, price)
    @isbn = isbn
    @price = Float(price)
  end

  def price_in_cents
    Integer(price*100 + 0.5)
  end

  def price_in_cents=(cents)
    @price = cents / 100.0
  end
end

---

Third file: stock-stats.rb

require 'csv-reader'
reader = CsvReader.new
ARGV.each do |csv_file_name|
  STDERR.puts "Processing #{csv_file_name}"
  reader.read_in_csv_data(csv_file_name)
end

puts "Total value = #{reader.total_value_in_stock}"

---

Fourth file: test_code.rb

# this is the test code file

require 'csv-reader'
require 'book-in-stock'
require 'stock-stats'

# code to call
reader = CsvReader.new
reader.read_in_csv_data("file1.csv")
reader.read_in_csv_data("file2.csv")

puts "Total value in stock = #{reader.total_value_in_stock}"


# code to call
book = BookInStock.new("isbn1", 33.80)
puts "Price = #{book.price}"
puts "Price in cents = #{book.price_in_cents}"
book.price_in_cents = 1234
puts "Price = #{book.price}"
puts "Price in cents = #{book.price_in_cents}"

---

CSV files: file1.csv

ISBN, Amount
isbn1, 49.00
isbn2, 24.54
isbn3, 33.23
isbn4, 15.55

file2.csv

ISBN, Amount
isbn5-file2, 39.98
isbn6-file2, 14.84
isbn7-file2, 43.63
isbn8-file2, 25.55

---

---

Edit

After Frederick Cheung's suggestion to change require to require_relative (for all but the 1st line of csv-reader.rb), the script is running, but a method is not working (see below)

(I did receive an error about this line: @price = Float(price) and changed it to @price = price.to_f and it runs just fine. )

3 Questions:

-> I changed the header of my csv files to "ISBN, Amount". Previously Amount was amount (not capitalized). Does this matter (i.e. the capitalizing of the header)?

-> While we're on the subject, what is the "row" keyword doing in the following #read_in_csv_data method?

-> Now that my code runs it appears that the output for "Total value in stock" is not summing up all of the prices in the csv file. Could a Rubyist please help me understand why this is happening?

The method

  def read_in_csv_data(csv_file_name)
    CSV.foreach(csv_file_name, headers: true) do |row|
      @books_in_stock << BookInStock.new(row["ISBN"], row["Amount"])
    end
  end

and call seem fine to me...

reader = CsvReader.new
reader.read_in_csv_data("file1.csv")
reader.read_in_csv_data("file2.csv")

Here is the current output from terminal:

Total value = []
Price = 33.8
Price in cents = 3380
Price = 12.34
Price in cents = 1234
Total value in stock = [#<BookInStock:0xb8168a60 @isbn="isbn1", @price=0.0>, #<BookInStock:0xb8168740 @isbn="isbn2", @price=0.0>, #<BookInStock:0xb8168358 @isbn="isbn3", @price=0.0>, #<BookInStock:0xb81546f0 @isbn="isbn4", @price=0.0>, #<BookInStock:0xb8156a18 @isbn="isbn5-file2", @price=0.0>, #<BookInStock:0xb8156784 @isbn="isbn6-file2", @price=0.0>, #<BookInStock:0xb81564a0 @isbn="isbn7-file2", @price=0.0>, #<BookInStock:0xb8156248 @isbn="isbn8-file2", @price=0.0>]

Thanks again.

Edit: Big thanks to 7Stud for a very thorough followup answer on every question I had. You have been exceptionally helpful. I have learned several important things thanks to your post.

Edit:

Still not able to get the code to run.

I am not sure how to add to / edit the $LOAD_PATH, so I tried putting all of the files into this directory: directory: ~MY_RUBY_HOME/lib/ruby/site_ruby/2.1.0/csv-reader (i.e. /Users/patrickmeaney/.rvm/rubies/ruby-2.1.1/lib/ruby/site_ruby/2.1.0/csv-reader)

However, I still receive the same error message:

 ✘  ~MY_RUBY_HOME/lib/ruby/site_ruby/2.1.0/csv-reader  ruby test_code.rb file1.csv file2.csv
/Users/patrickmeaney/.rvm/rubies/ruby-2.1.1/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require': cannot load such file -- ./csv_reader (LoadError)
    from /Users/patrickmeaney/.rvm/rubies/ruby-2.1.1/lib/ruby/site_ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
    from test_code.rb:1:in `<main>'

Answer 1

require searches for files in Ruby's load path (this is stored in the global variables $: or $LOAD_PATH)

The current directory is not in the load path by default (it used to be in ruby 1.8 and earlier) which is why ruby says that it can't find csv-reader

You can add to the load path either by manipulating the $: variable (it behaves just like an array) or with the the -I option.

For example if you launch irb by doing

irb -I.

Then your code should run without modification (assuming there are no other problems with it)

Lastly you could switch your require statements to use require_relative - this locates files relative to the current file

Answer 2

I have written some code out of the Ruby Pickaxe book

Yeah, but there are many Ruby Pickaxe books.

IRB command, followed by the error message it generates:

NEVER run anything in IRB. Never use IRB for ANYTHING. Instead put your code in a file, and then run the file, e.g:

$ ruby my_prog.rb

LoadError: cannot load such file -- csv-reader

If the files you want to require are not located in the directories ruby searches automatically(to see those directories execute the line `p $LOAD_PATH'), then you can specify the absolute or relative path to the file you want to require in the require statement:

require './book_in_stock'

I did receive an error about this line: @price = Float(price) and changed it to @price = price.to_f and it runs just fine.

x = 'hello'
p x.to_f
p Float(x)

--output:--
0.0
1.rb:3:in `Float': invalid value for Float(): "hello" (ArgumentError)
    from 1.rb:3:in `<main>

The difference between Float() and to_f() is that Float will raise an exception when it is unable to convert the String to a Float, while to_f() will return 0 when it cannot convert the String to a Float. Unless you know what you are doing, it's probably best to use Float(), so that you are alerted to the fact that your data has an error in it.

While we're on the subject, what is the "row" keyword doing in the following #read_in_csv_data method?

When you loop through the rows of your file(e.g. CSV.foreach), csv converts one row of your file into a thing called a "CSV::Row", and then assigns the "CSV::ROW" object to the loop variable, which you have named "row":

CSV.foreach(csv_file_name, headers: true) do |row|
                                               ^
                                               |

So "row" is a variable that refers to a "CSV::Row". A "CSV::Row" acts like a hash, enabling you to write things like row['ISBN'] to retrieve the value in that column.

Spaces are significant in csv files. If your header row is ISBN, Amount, then the column names are "ISBN" and " Amount" (see the leading space?). That means there is no value for

row['Amount']

i.e. it will return nil, but there is a value for

row[' Amount']
     ^
     |

Now that my code runs it appears that the output for "Total value in stock" is not summing up all of the prices in the csv file. Could a Rubyist please help me understand why this is happening?

1) A def returns the value of the last statement that was executed in the def.

2) Array#each() returns the array.

Here is your def:

  def total_value_in_stock
    sum = 0.0
    @books_in_stock.each {|book| sum += book.price}
  end

That def returns the @books_in_stock array. You need to return the sum:

  def total_value_in_stock
    sum = 0.0
    @books_in_stock.each {|book| sum += book.price}
    sum
  end

If you want to get tricky, you can have csv automatically convert any data in your file that looks like a number to a number:

CSV.foreach(
  csv_file_name, 
  headers: true,
  :converters => :numeric
) do |row| ...

...then your BookInStock class would look like this:

class BookInStock
  attr_reader :isbn
  attr_accessor :price

  def initialize(isbn, price)
    @isbn = isbn
    @price = price  #Float(price)
  end

Here are all your files amended so they will run correctly:

csv_reader.rb:

require 'csv'
require './book_in_stock'

class CsvReader

  def initialize
    @books_in_stock = []
  end

  def read_in_csv_data(csv_file_name)
    CSV.foreach(csv_file_name, headers: true) do |row|
      @books_in_stock << BookInStock.new(row["ISBN"], row["Amount"])
    end
  end

  def total_value_in_stock
    sum = 0.0
    @books_in_stock.each {|book| sum += book.price}
    sum
  end

  def number_of_each_isbn
  end

end

stock_stats.rb:

require './csv_reader'

reader = CsvReader.new

ARGV.each do |csv_file_name|
  STDERR.puts "Processing #{csv_file_name}"
  reader.read_in_csv_data(csv_file_name)
end

puts "Total value = #{reader.total_value_in_stock}"

test_code.rb:

require './csv_reader'
require './book_in_stock'
require './stock_stats'

reader = CsvReader.new
reader.read_in_csv_data("file1.csv")
reader.read_in_csv_data("file2.csv")

puts "Total value in stock = #{reader.total_value_in_stock}"


# code to call
book = BookInStock.new("isbn1", 33.80)
puts "Price = #{book.price}"
puts "Price in cents = #{book.price_in_cents}"
book.price_in_cents = 1234
puts "Price = #{book.price}"
puts "Price in cents = #{book.price_in_cents}"

book_in_stock.rb:

class BookInStock
  attr_reader :isbn
  attr_accessor :price

  def initialize(isbn, price)
    @isbn = isbn
    @price = Float(price)
  end

  def price_in_cents
    Integer(price*100 + 0.5)
  end

  def price_in_cents=(cents)
    @price = cents / 100.0
  end
end

file1.csv:

ISBN,Amount
isbn1,49.00
isbn2,24.54
isbn3,33.23
isbn4,15.55

file2.csv:

ISBN,Amount
isbn5-file2,39.98
isbn6-file2,14.84
isbn7-file2,43.63
isbn8-file2,25.55

Now run the program:

~/ruby_programs$ ruby test_code.rb file1.csv file2.csv
Processing file1.csv
Processing file2.csv
Total value = 246.32
Total value in stock = 246.32
Price = 33.8
Price in cents = 3380
Price = 12.34
Price in cents = 1234