From: Mark Hubbart <discordantus@...>
Date: 2004-10-09T01:36:51+09:00
Subject: Re: A sort_by descending sort

On Sat, 9 Oct 2004 00:55:14 +0900, Michael Gaunnac
<mlgaunnac@hotmail.com> wrote:
> 
> 
> gabriele renzi wrote:
> > Michael Gaunnac ha scritto:
> >
> >> Perhaps this has already been covered, but I discovered this idiom
> >> for doing a descending sort using sort_by.
> >
> > why not:
> >  >> [1,2.0,6,23 ,546,421.1,,0.1].sort_by {|x| 1-x}
> > => [546, 421.1, 23, 6, 2.0, 1, 0.1]
> >
> > Anyway, thankx for making me think of this :)
> 
> More context:
> 
> arr = %W{
> A10/04/200420:30
> A10/04/200405:00
> A10/04/200420:00
> A10/06/200405:00
> A10/07/200409:37
> A10/07/200419:00
> A10/07/200421:30
> E10/08/200404:00
> A10/08/200407:50
> A10/08/200405:15
> D10/08/200404:00
> A10/08/200305:00
> A10/08/200405:00
> A10/08/200403:55
> B10/08/200404:15
> A10/07/200419:30
> A10/07/200422:00
> B10/07/200405:00
> B10/08/200407:50
> A10/08/200407:50
> A10/08/200407:25
> C10/08/200404:00
> B10/08/200404:00
> A10/08/200404:45
> A10/08/200404:10
> B10/08/200404:10
> A10/08/200404:00
>        }
> # sort                         ascending      descending  year
> descending  month/day                          descending hour:minute
> arr = arr.sort_by {|i| [[i.slice(0,1)],
> [i.slice(7,4).tr('0-9','9876543210')],
> [i.slice(1,5).tr('/0-9','/9876543210')],
> [i.slice(11,5).tr(':0-9',':9876543210')]]}
> 
> arr.each {|i| print i, "\n"}
> 
> <challenge>
> Can this sort be simplified (with Ruby of course)?
> </challenge>

assuming an unchanging format, perhaps:

arr = arr.sort_by do |i|
  i.scan(/(.)(..).(..).(....)(..):(..)/).map do |a,*date|
    m,d,y,h,n = *date.map{|x| x.to_i}
    [a,-y,-m,-d,-h,-n]
  end
end

cheers,
Mark