ruby on rails - How do I determine if a string is numeric?

Question

I thought this would be easier to find, but I'm quite surprised that it isn't.

How on Earth do I test if a string is a number (including decimals) outside a Model?

e.g.

is_number("1") # true
is_number("1.234") # true
is_number("-1.45") # true
is_number("1.23aw") #false

In PHP, there was is_numeric, but I can't seem to find an equivalent in Ruby (or Rails).

So far, I've read the following answers, and haven't gotten any closer:

• Ruby on Rails - Validate a Cost
• Ruby/Rails - How can you validate against decimal scale?
• invalid decimal becomes 0.0 in rails

Answer 1

You could borrow the idea from the NumericalityValidator Rails uses to validate numbers, it uses the Kernel.Float method:

def numeric?(string)
  # `!!` converts parsed number to `true`
  !!Kernel.Float(string) 
rescue TypeError, ArgumentError
  false
end

numeric?('1')   # => true
numeric?('1.2') # => true
numeric?('.1')  # => true
numeric?('a')   # => false

It also handles signs, hex numbers, and numbers written in scientific notation:

numeric?('-10')   # => true
numeric?('0xFF')  # => true
numeric?('1.2e6') # => true