Ruby - create unknown amount of variables from file

Question

This might be hard to explain, but I'll try.

Let's say I have a text file containing:

variable one
I'm variable 2
300
False
I am variable 5

Let's assume that I have multiple files like this and I don't know what is in each file. I want to take each line in the file and put it into a variable.

For example, this file would become these variables (which I can sort into strings, numbers and booleans with if statements):

var1 = "variable one"
var2 = "I'm variable 2"
var3 = 300
var4 = False
var5 = "I am variable 5"

I want to make sure that this can be applied to any file with any number of lines.

Here's an example of what I hope the code would look like:

File.open("file.txt").each do |line|
  var.new = "var" + line.line_number #creates new variable named "var" and the line number
var = line
end

I hope someone understands and knows how to do this because I'm completely stumped. I feel like there's some sort of really simple solution here that everybody commonly knows and I'm missing it or I just don't know it.

Thanks, Reece

What do you intend to do with them afterwards? You cannot dynamically create local variables but depending on your end goal there are lots of ways to implement this — engineersmnky, Aug 21 '18 at 20:12

score 1 · Accepted Answer · answered Aug 21 '18 at 20:23

1

This answers your question, but context is certainly required to do this in a way that actually matters to your application.

This isn't necessarily the only way, or even the "best" way, but it's the most straightforward in my opinion:

File.read("file.txt").split("\n").each_with_index do |line, index|
  instance_variable_set("@var#{index}", line) 
end

@var0 #variable one
@var1 #I'm variable 2

If you want to convert False and 300 from a string — which is how it's read from the file — to a ruby object, you'd have to do some manual parsing. Say,

def content_for_line(line)
  if line == 'False'
    return false
  end
  if line.to_s == line.to_i.to_s
    return line.to_i 
  end
  line
end

...

instance_variable_set("@var#{index}", content_for_line(line))

Maybe you only want to read the file as an array though.

array = File.read("file.txt").split("\n")

array[0] #variable one

answered Aug 21 '18 at 20:23

Josh Brody

5,153
1
14
25

Thank you very much. I've been struggling with this for a while now, finally, I've got it. Once again, thanks. – notsoscottishscot Aug 21 '18 at 20:35
Just wondering: how would I then be able to print every variable? – notsoscottishscot Aug 21 '18 at 20:52
@Voidableryzer `self.instance_variables` will list all instance variables as an array. you can loop through them and print the ones you want, a la `self.instance_variables.select { |var| var.index("var") }.each { |var| puts instance_variable_get(var) }` – Josh Brody Aug 22 '18 at 03:33
Ok, thanks for the help. – notsoscottishscot Aug 22 '18 at 07:31

score 0 · Answer 2 · answered Aug 21 '18 at 20:19

0

It feels like you really want an array here. To that end you can read the file directly into an array, one entry per line:

array_of_lines = File.readlines("file.txt")
array_of_lines[0]
=> "variable one\n"
array_of_lines[1]
=> "300\n"

etc

answered Aug 21 '18 at 20:19

elliotcm

760
4
7

score 0 · Answer 3 · answered Aug 21 '18 at 20:41

You could implement this as as class with built in parsing logic (I only handled the given example):

class VarGroup
  attr_reader :vars
  def initialize(file_name)
    @vars = File.foreach(file_name).map do |l|
      if l =~ /(True|False)/i
        l.match?(/True/i)
      else  
        begin  
          Integer(l)
        rescue ArgumentError 
          l.strip
        end  
      end
    end
  end

  def method_missing(method_name,*args,&block)
    if method_name =~ /var(\d+)/ && $1.to_i.nonzero? && $1.to_i <= vars.size
      @vars[$1.to_i - 1] 
    else 
      super
    end
  end
end

Then it can be called like

v = VarGroup.new('test.txt')
v.vars 
#=> ["variable one", "I'm variable 2", 300, false, "I am variable 5"]
(1..6).each do |n|
  p v.public_send("var#{n}")
end
# "variable one"
# "I'm variable 2"
# 300
# false
# "I am variable 5"
# undefined method `var6' for #<VarGroup:0x000055a23e2f64e0>

Ruby - create unknown amount of variables from file

3 Answers3