Question

Developing a little survey webapp, ran into problem that deals with ranges for rating type questions.
So a rating’s range could be:

1..10
-5..0
-5..5
'a'..'z'
'E'..'M'

and so on

The range is stored as a pair of varchars in database (start and end of range). So range always starts off as a string input.

What is the best way to take these string values and build a Ruby Range accordingly.
I can’t just go value.to_i as this won’t work for string iteration. Having a bunch of if’s seems ugly. Any better way?

Not as important, but worth asking:
Also what if I wanted to make it all work with reversed range? Say 5-to-0 or G-to-A. I know that Ruby doesn’t support reverse range (since it uses succ() to iterate). What would be the best way here?

Thanks in advance!

Update:

Based on Wouter de Bie’s suggestion I’ve settled for this:

def to_int_or_string(str)
  return str.match(/^-?\d+$/) ? str.to_i : str.strip
end

def ratings_array(from, to)
  from = to_int_or_string(from)
  to = to_int_or_string(to)
  from > to ? Range.new(to, from).to_a.reverse : Range.new(from, to).to_a
end

Any thoughts?

Answer 1

Use Range.new:

Range.new("a","z")
=> "a".."z"

Range.new(-5,5)
=> -5..5

If you’re varchars contain quotes, you can use eval to get the right ranges:

from = "'a'"
to = "'z'"
eval("Range.new(#{from},#{to})")

Otherwise you could use value.to_i to figure out if it was a number or a string in the varchar:

a = "x"
a = (a.to_i == 0 && a != "0") ? a : a.to_i
=> "x"

a = "5"
a = (a.to_i == 0 && a != "0") ? a : a.to_i
=> 5

Which of course can be nicely extracted into a method:

def to_int_or_string(value)
  return (value.to_i == 0 && value != "0") ? value : value.to_i
end

def to_range(from, to)
  return Range.new(to_int_or_string(from), to_int_or_string(to))
end

To reverse your range, you have to convert it to an array first:

Range.new("a","g").to_a.reverse
=> ["g", "f", "e", "d", "c", "b", "a"]