How do I iterate over a file? - ruby

Question

I have a file that looks like this:
[noahc:~/projects/wordsquares] master(+87/-50)* ± cat wordlist/test_word_list.txt
card
apple
joe
bird
card
dart
area
rear
birdbird
after
boat
swim
north
abbe
byes
beep
If I open up an irb session, I can do:
2.0.0p247 :001 > file = File.open('./wordlist/test_word_list.txt', 'r')
=> #<File:./wordlist/test_word_list.txt>
2.0.0p247 :002 > file.readlines
=> ["card\n", "apple\n", "joe\n", "bird\n", "card\n", "dart\n", "area\n", "rear\n", "birdbird\n", "after\n", "boat\n", "swim\n", "north\n", "abbe\n", "byes\n", "beep \n", "\n"]
But, now I have a class called WordSquareGenerator:
class WordSquareGenerator
require 'pry'
require 'pry-nav'
require './lib/word_list_builder.rb'
def initialize(n, file_location)
#size_of_square = n
#file = load_file(file_location)
#word_stem_hash = WordListBuilder.new(n, #file).word_stem_hash
#word_list = nil
end
def word_square_word_list
binding.pry
#file.each do |w|
binding.pry
#word_list ? break : solve_for_word_list([word])
end
binding.pry
end
def is_list_valid?(list)
(0..#size_of_square - 1).each do |n|
(0..#size_of_square - 2).each do |m|
return false if list[n][m] != list [m][n]
end
end
#generated_list = list unless #generated_list
end
def solve_for_word_list(word_array)
if word_array.length == 4
#word_list = word_array
elsif #word_list
else
next_words = #word_stem_hash[word_array.map{|w| w[word_array.length]}.join]
next_words.each do |word|
solve_for_word_list(word_array + [word])
end
end
end
private
def load_file(file_location)
File.open(file_location, 'r')
end
end
When I run the word_square_word_list method and hit the first binding.pry, I can do:
2.0.0 (#<WordSquareGenerator:0x007ff3f91c16b0>):0 > #file.readlines
=> []
and I get an empty array for readlines. How can it be that I'm getting two different results doing the same thing, except one is inside that class and the other isn't?

Answer 1

At WordListBuilder you are probably reading the file already and when the action gets back to WordSquareGenerator the file is already at it's end and there's nothing else to read. First, don't do what you're doing now, that is opening the file since this leaks the file handle (you're not closing it anywhere) and someone else reading the handle is causing your code to fail.
Here's how you could do it:
class WordSquareGenerator
require 'pry'
require 'pry-nav'
require './lib/word_list_builder.rb'
def initialize(n, file_location)
#size_of_square = n
#file_location = file_location
#word_stem_hash = WordListBuilder.new(n, file_location).word_stem_hash
#word_list = nil
end
def word_square_word_list
binding.pry
IO.foreach(#file_location) do |word|
binding.pry
#word_list ? break : solve_for_word_list([word])
end
binding.pry
end
def is_list_valid?(list)
(0..#size_of_square - 1).each do |n|
(0..#size_of_square - 2).each do |m|
return false if list[n][m] != list [m][n]
end
end
#generated_list = list unless #generated_list
end
def solve_for_word_list(word_array)
if word_array.length == 4
#word_list = word_array
elsif #word_list
else
next_words = #word_stem_hash[word_array.map{|w| w[word_array.length]}.join]
next_words.each do |word|
solve_for_word_list(word_array + [word])
end
end
end
end
And you would also need to update WordListBuilder to do the same. This also has the advantage of closing the file handle automatically for you so you don't have to care about closing it yourself.

Answer 2

Try running this before you read the lines:
#file.seek 0
You have probably already read the lines, and you have to seek back to the start of the file before you read them again.
Sample IRB session:
irb(main):001:0> f = File.new 'test.txt' # already existing file
=> #<File:test.txt>
irb(main):002:0> f.readlines
=> ["this", "is", "a", "test"]
irb(main):003:0> f.readlines
=> []
irb(main):004:0> f.seek 0
=> 0
irb(main):005:0> f.readlines
=> ["this", "is", "a", "test"]
You could even make it a method:
def readlines
#file.seek 0
#file.readlines
end
Also, make sure to close your file (#file.close)! You should only leave it open for as little time as possible. And you definitely should not leave it open for the whole program. If you don't want to worry about that, just store the lines in a variable instead of keeping the file:
#lines = File.open(file_location) {|f|
f.readlines
}
# you could also use the shortcut form
# #lines = File.open(file_location, &:readlines)