Natural order comparison of two strings

natcmp.rb

# natcmp.rb
#
# Natural order comparison of two strings
# e.g. "my_prog_v1.1.0" < "my_prog_v1.2.0" < "my_prog_v1.10.0"
# which does not follow alphabetically
#
# Based on Martin Pool's "Natural Order String Comparison" originally written in C
# http://sourcefrog.net/projects/natsort/
#
# This implementation is Copyright (C) 2003 by Alan Davies
# <cs96and_AT_yahoo_DOT_co_DOT_uk>
#
# This software is provided 'as-is', without any express or implied
# warranty.  In no event will the authors be held liable for any damages
# arising from the use of this software.
#
# Permission is granted to anyone to use this software for any purpose,
# including commercial applications, and to alter it and redistribute it
# freely, subject to the following restrictions:
#
# 1. The origin of this software must not be misrepresented; you must not
#    claim that you wrote the original software. If you use this software
#    in a product, an acknowledgment in the product documentation would be
#    appreciated but is not required.
# 2. Altered source versions must be plainly marked as such, and must not be
#    misrepresented as being the original software.
# 3. This notice may not be removed or altered from any source distribution.

class String

# 'Natural order' comparison of two strings
def String.natcmp(str1, str2, caseInsensitive=false)
        str1, str2 = str1.dup, str2.dup
	compareExpression = /^(\D*)(\d*)(.*)$/

	if caseInsensitive
		str1.downcase!
		str2.downcase!
	end

	# Remove all whitespace
	str1.gsub!(/\s*/, '')
	str2.gsub!(/\s*/, '')

	while (str1.length > 0) or (str2.length > 0) do
		# Extract non-digits, digits and rest of string
		str1 =~ compareExpression
		chars1, num1, str1 = $1.dup, $2.dup, $3.dup

		str2 =~ compareExpression
		chars2, num2, str2 = $1.dup, $2.dup, $3.dup

		# Compare the non-digits
		case (chars1 <=> chars2)
			when 0 # Non-digits are the same, compare the digits...
				# If either number begins with a zero, then compare alphabetically,
				# otherwise compare numerically
				if (num1[0] != 48) and (num2[0] != 48)
					num1, num2 = num1.to_i, num2.to_i
				end

				case (num1 <=> num2)
					when -1 then return -1
					when 1 then return 1
				end
			when -1 then return -1
			when 1 then return 1
		end # case

	end # while

	# Strings are naturally equal
	return 0
end

end # class String