Array range being recognised as string - unable to convert to integer - ruby-on-rails

Question

i've written a function within a model to scrape a site and store certain attributes within a separate model (story):
def get_content
request = HTTParty.get("#{url}")
doc = Nokogiri::HTML(request.body)
doc.css("#{anchor}")["#{range}"].each do |entry|
story = self.stories.new
story.title = entry.text
story.url = entry[:href]
story.save
end
This uses the url, anchor, and range attributes of a Sections variable. The range attribute is stored as an array range - i.e. 0..2 or 11..13 - however, I'm being told that it can't convert a string into a variable. I've tried storing range as an integer and as a string, but both fail.
I realise I could input the beginning and end of the range as two separate integers in my db, and put ["#{beginrange}".."#{endrange}"] but this seems a messy way of doing it.
Any other ideas? Many thanks in advance

Answer 1

Hmm if you are sure that the range is always a string like '1..2' ('<Integer >..<Integer>'), you can use the eval method:
In my IRB console:
1.9.3p0 :032 > (eval "1..2").each { |l| puts l }
1
2
=> 1..2
1.9.3p0 :033 > (eval "1..2").inspect
=> "1..2"
1.9.3p0 :034 > (eval "1..2").class
=> Range
In your case:
doc.css("#{anchor}")[eval(range)].each do |entry|
#...
end
But eval is kind of dangerous. If you are sure that the range attribute is a Range as a String (validations and Regex are here to help), you can use eval without risk.

Answer 2

There's a couple things I see wrong.
["#{beginrange}".."#{endrange}"] creates a range of characters, not a range of integers, which Array[] needs:
beginrange = 1
endrange = 2
["#{beginrange}".."#{endrange}"]
=> ["1".."2"]
[beginrange..endrange]
=> [1..2]
But, you're storing the representation of the array range you need as a string. If I had a string representation of a range, I'd use this:
range_value = '1..2'
[Range.new(*range_value.scan(/\d+/).map(&:to_i))]
=> [1..2]
Or, if there was a chance I'd encounter an exclusive-range:
[Range.new(*range_value.scan(/\d+/).map(&:to_i), range_value['...'])]
=> [1..2]
range_value = '1...2'
[Range.new(*range_value.scan(/\d+/).map(&:to_i), range_value['...'])]
=> [1...2]
Those are all good when you can't trust your Range string representation's source, i.e., the value is coming from a form or a file someone else created. If you own the incoming value, or, for convenience, stored it as a string in a database, you can easily recreate the range using eval:
eval('1..2').class
=> Range
eval('1..2')
=> 1..2
eval('1...2')
=> 1...2
People are afraid of eval, because, used unwisely, it is dangerous. That doesn't mean we should avoid using it, instead, we should use it when it's safe.
You could use a regex to check the format of the string, raise an exception if it's not acceptable, then continue:
raise "Invalid range value received" if (!range_value[/\A\d+\s*\.{2,3}\s*\d+\z/])
[eval(range_value)]