From: Brian Candler <B.Candler@...>
Date: 2004-10-08T23:32:22+09:00
Subject: Re: A sort_by descending sort

On Fri, Oct 08, 2004 at 10:57:20PM +0900, Michael Gaunnac wrote:
> Perhaps this has already been covered, but I discovered this idiom for doing a descending sort using sort_by.
> 
> arr = Array.new
> (0..20).each {|i| arr.push sprintf('%02d', i)}
> p arr
> #=>["00", "01", "02", "03", "04", "05", "06", "07", "08", "09", "10", "11", "12", "13", "14", "15", "16", "17", "18", "19", "20"]
> 
> arr = arr.sort_by {|i| [i.slice(0,2).tr('0-9','9876543210')]}  # descending sort using 9's complement
> 
> p arr
> #=>["20", "19", "18", "17", "16", "15", "14", "13", "12", "11", "10", "09", "08", "07", "06", "05", "04", "03", "02", "01", "00"]

arr2 = arr1.sort.reverse!
or
arr2 = arr1.sort_by { |i| ... }.reverse!

I'd guess that would be quicker and less memory-hungry than generating
temporary string objects with translated characters in them.

Regards,

Brian.