RCR 268: String.natcmp

Computer string sorting algorithms generally don't order strings containing numbers in the same way that a human would do. Consider:

  rfc1.txt
  rfc2086.txt
  rfc822.txt

It would be more friendly if the program listed the files as

  rfc1.txt
  rfc822.txt
  rfc2086.txt

Filenames sort properly if people insert leading zeros, but they don't always do that.

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

class String

1. '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