From: Robert Klemme <shortcutter@...>
Date: 2009-05-19T15:15:03+09:00
Subject: Re: Sorting numbers as strings

On 19.05.2009 02:55, Rob Biedenharn wrote:
> On May 18, 2009, at 1:01 PM, Robert Klemme wrote:
> 
>> On 18.05.2009 17:37, Rob Biedenharn wrote:
>>
>>> If you do need to consider things like "FastEthernet..." v.   
>>> "GigabitEthernet...", then perhaps you want something like this  
>>> which  breaks the original string into digits and non-digits and  
>>> converts the  digits to be integers.
>>> puts DATA.sort_by {|s| s.scan(/\d+|\D+/).map {|x| x =~ /\d+/ ?   
>>> x.to_i : x } }
>> Good point!  Here's an interesting variant:
>>
>> puts DATA.sort_by {|s| s.scan(/(\d+)|\D+/).map { $1 ? $1.to_i : $& } }

> Interesting, but "wrong" in that it doesn't sort the way the OP wanted.
> Actually, since all the regexp applications have been applied by #scan  
> before the #map happens, the values of $1 and $& are effectively  
> constants and no sorting happens at all.

Aaargh!  Yes, you are completely right.

> However, that did inspire me to make my version a little better.
> 
> puts DATA.sort_by {|s| s.scan(/(\d+)|(\D+)/).map {|(n,s)| s ||  
> n.to_i } }
> 
> I'd rather make the variables local than invoke the Perlish Regexp  
> globals (even if they did were assigned in the block the way you  
> expected).  It could be even more readable if (n,s) were replaced with  
> (digits,nondigits), but it looks OK to me with n and s.

Absolutely agree, I try to use local variables whenever possible. 
Although I recently learned that $1 etc. are local to the current stack 
frame!  I did not knew that before and it certainly makes their use a 
lot safer.

Thanks for catching my mistake!

Kind regards

	robert

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