From: dblack@...
Date: 2003-05-04T02:18:44+09:00
Subject: Re: Cross platform `ls -t`

Hi --

On Sun, 4 May 2003, Hal E. Fulton wrote:

> ----- Original Message -----
> From: "gabriele renzi" <surrender_it@rc1.vip.lng.yahoo.com>
> Newsgroups: comp.lang.ruby
> To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
> Sent: Saturday, May 03, 2003 11:31 AM
> Subject: Cross platform `ls -t`
>
>
> > Is there a way using Dir to have a list of directory entries sorted by
> > time?
> >
> > What I'd like to have is a `ls -t` that works even on windows
> > (and no, I don't want ls.exe ;)
>
> Mmm. Something like this (untested):
>
>   list = Dir["**"].sort {|x,y| File.stat(x).mtime < File.stat(y).mtime }
>
> Of course, it's inefficient -- a Schwartzian transform
> would make it faster.

Procrastinating on real work, I tried it out:

  require 'benchmark'
  include Benchmark

  n = 1000

  bm do |b|
    b.report("Non-Schwartzian:\n") do
      n.times {
	Dir["**"].sort {|x,y|
        # (Put y test first to duplicate order of ls -t)
	  File.stat(y).mtime <=> File.stat(x).mtime
	}
      }
    end
    b.report("Schwartzian:\n") do
      n.times {
	Dir["**"].map {|f|
	  [File.stat(f).mtime,f]
	}.sort {|x,y|
	  y[0] <=> x[0]
	}.map{|a|
	  a[1]
	}
      }
    end

Output:

	user     system      total        real
  Non-Schwartzian:
    7.560000   2.260000   9.820000 (  9.827662)
  Schwartzian:
    4.150000   0.260000   4.410000 (  4.422282)


Cool :-)


David

-- 
David Alan Black
home: dblack@superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav