What is the best way to determine if a variable is a number in Ruby?

Question

Possible Duplicate:
Test if string is a number in Ruby on Rails

Currently I have this (awful) code:

def is_num(num_given)
  begin
    num_given.to_i
    worked = true
  rescue
    worked = false
  ensure
    return worked
  end
end

Which I refactored to this:

def is_num(num_given)
  num_given.to_i.is_a?(Numeric) rescue false
end

This still just doesn't feel right to me, is there a better way to do this?

Both of these implementations work fine for my purposes, I am just looking for some code euphoria.

Answer 1

something.is_a?(Numeric) is the way to go. Referring to your latter example, there's no need to call to_i on the input.

Note that something.is_a?(Numeric) will not work if you're looking to see if a string is a number...

Answer 2

Here's another solution. It's not very Ruby-like, but that's intentional (e.g., while is faster than str.chars.each in this case).

# is a character between 0 and 9? (based on C's isdigit())
def digit?(c)
  o = c.ord
  o >= 48 && o <= 57 # '0'.ord, '9'.ord
end

# is a string numeric (i.e., represented as an integer or decimal)?
def numeric?(str)
  str = str.to_s unless str.is_a?(String)
  l = str.length
  i = 0

  while i < l
    c = str[i]
    if c == '.' || c == '-'
      i += 1
      next
    end

    return false if !digit?(c)

    i += 1
  end

  true
end

Here are the unit tests. Let me know if I missed a case. For other answerers, just change the subject block to your function.

if $0 == __FILE__
  require 'minitest/autorun'
  describe :digit? do
    %w(- + : ? ! / \ ! @ $ ^ & *).each do |c|
      it "flunks #{c}" do
        digit?(c).must_equal false
      end
    end

    %w(0 1 2 3 4 5 6 7 8 9).each do |c|
      it "passes #{c}" do
        digit?(c).must_equal true
      end
    end
  end

  describe :numeric? do
    subject { :numeric? }
    %w(0 1 9 10 18 123.4567 -1234).each do |str|
      it "passes #{str}" do
        method(subject).call(str).must_equal true
      end
    end

    %w(-asdf 123.zzz blah).each do |str|
      it "flunks #{str}" do
        method(subject).call(str).must_equal false
      end
    end

    [-1.03, 123, 200_000].each do |num|
      it "passes #{num}" do
        method(subject).call(num).must_equal true
      end
    end
  end
end

Answer 3

The functions you listed won't work:

is_num("a") #=> true

The problem is that they don't raise an error for invalid input. What you want is Integer, which will raise an error which you can rescue:

def is_num(num_given)
  !!Integer(num_given) rescue false
end

This works:

irb(main):025:0> is_num("a")
=> false
irb(main):026:0> is_num(5)
=> true
irb(main):027:0> is_num((1..2))
=> false
irb(main):028:0> is_num("3")
=> true

(There may be a more natural way to do this, though.)

Answer 4

You can always use a simple regex:

def is_num(num_given)
  num_given =~ /\d+(\.\d+)?/
end