From: Stefano Crocco <stefano.crocco@...>
Date: 2007-03-15T02:42:59+09:00
Subject: Re: Copying files and changing their names

Alle mercoled狸 14 marzo 2007, Sam Fent ha scritto:
> Stefano Crocco wrote:
> > NOT TESTED - make a trial with some useless directory before using it on
> > real
> > data
>
> Hi Stefano (anzi, 'ciao!'),
>
> Thank you very much -- that has helped me tremendously. I have one
> further question though. What if, instead of the number "9", I wanted to
> copy the file with the HIGHEST number.
>
> For example, my files might be
>
> example1.txt
> example2.txt
> test1.txt
> test2.txt
> test3.txt
>
> If I wanted to change example2.txt to example-final.txt, and test3.txt
> to test-final.txt, how could I iterate throught the files to find the
> file with the highest number?
>
> Grazie mille per qualsiasi aiuto,
> Sam

This should work:

require 'find'
require 'set'
require 'file_utils'

Find.find('.') do |f|
  # consider only directories, we'll take care of files later	
  if File.directory?(f)
    # create a Set containing the names of the files in the directory f [1]
    entries=Set.new(Dir.entries(f).reject{|e| File.directory?(e)})
    #separate the files basing on their basename (the part before -number) [2]
    names=entries.classify{|e| e.match(/^.*-\d+$/)[1]}
    # for each of the basenames
    names.each_value do |v|
      # sort the set basing on the number and select the last
      name=v.sort_by{|n| n.match(/-(\d+)/)[1].to_i}.last
      # copy it to the new name. name is relative to f, so we prepend it
      FileUtils.cp "#{f}#{name}", "#{f}#{name.sub(/-\d+$/, '-final')}"
     end
  end
end

The line marked by [2] creates a hash of sets, each of them containing the 
files with the same basename. This method is the only reason to use a set in 
line [1], instead of keeping the array. For instance, if the directory f 
contains the files
a-1
a-2
a-3
b-1
b-2
c-1
c-2
c-3
c-4

the result of line [2] will be a hash with keys 'a', 'b' and 'c'. The keys 'a' 
will contain a set with elements 'a-1', 'a-2', 'a-3', and so on for the other 
keys.

Stefano