From: Josef 'Jupp' Schugt <jupp@...>
Date: 2008-10-30T21:47:10+09:00
Subject: Re: Sorting Array Of Dates

On Thu, 30 Oct 2008 02:27:32 +0100, Chandu Chandu <chandu_750@yahoo.com>  
wrote:

> Hi, Everyone I am a newbie to ruby....
>
> just started with some examples
>
> i have array
>
> date = ['12/09/2007','06/06/2004','10/06/2005']
>
> i wanted to sort dates in ascending order i.e
> ['06/06/2004','10/06/2005','12/09/2007']

you forgot to mention if the date format is reasonable (dd/mm/yyyy) or not  
(mm/dd/yyyy) - reasonable in the sense that the parts have an ascending or  
descending significance and not an arbitrary one.

Anyway, here's a solution for both cases:

def datecmp(a, b, reasonable = true)
   arra, arrb = a.split('/'), b.split('/')
   cmp = (arra[2] <=> arrb[2])
   return cmp if (cmp = (arra[2] <=> arrb[2])) != 0
   if reasonable
     (cmp = (arra[0] <=> arrb[0])) != 0 ? cmp : (arra[1] <=> arrb[1])
   else
     (cmp = (arra[1] <=> arrb[1])) != 0 ? cmp : (arra[0] <=> arrb[0])
   end
end

date = ['12/01/2007', '11/02/2007', '11/11/2005']
puts "reasonable date format"
puts date.sort { |a, b| datecmp(a, b) }
puts "\nno reasonable date format"
puts date.sort { |a, b| datecmp(a, b, false) }

that results in

reasonable date format
11/11/2005
11/02/2007
12/01/2007

no reasonable date format
11/11/2005
12/01/2007
11/02/2007

but besides that the normal date format is yyyy-mm-dd.

I don't know about the situation in other countries but in Germany the  
date format you SHOULD use (in an RFC sense, the DIN standard says so) is  
that ISO standard form. Other formats are only tolerable but not  
desireable. Which does not mean that many Germans use that format. You  
hear me frequently protest against forms that still use antiquated date  
formats :)

Josef 'Jupp' Schugt
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