From: Robert Klemme <bob.news@...>
Date: 2003-08-08T00:26:08+09:00
Subject: Re: Elegant solution for a loop-break problem


"KONTRA Gergely" <kgergely@mlabdial.hit.bme.hu> schrieb im Newsbeitrag
news:20030807141710.GE7040@mlabdial.hit.bme.hu...
> Hi!
>
> I've tried to write a little program, which detect duplicate files.
> My way to solve this is to have a hash for the known files like this
> { fileSize  => [[file1,file2],[file3,file4]],
>   fileSize2 => [[file6,file7]] }
>
> So, file1..file4 have the same size, file1 and file2's content is
> identical, similarly file3 and file4 is identical.
>
> First, the Hash is empty, and then I insert the files to be examined,
> like this.
>
> files = Hash.new { [] }
> for filename in filesToBeAdded
>   filesize=File.filesize(filename)
>   for fn in filename[filesize]
>     if equalContent(fn[0], filename)
>       # add this file to this 'segment' TODO: alter files
>       # next 'filename in filesToBeAdded'
>     end
>   end
>   # if loop exited normally, create a new segment
> end

Often the best solution is to use modularization for such problems. It
makes code more readable and easier to maintain:

def addToGroup(group, filename)
  for fn in group
    if equalContent(fn[0], filename)
      # add this file to this 'segment' TODO: alter files
      # next 'filename in filesToBeAdded'
      fn << filename
      return
    end
  end
  # if loop exited normally, create a new segment
  group << [filename]
end

# or, a bit more rubish

def addToGroup(group, filename)
  group.each do |fn|
    if equalContent(fn[0], filename)
      # add this file to this 'segment' TODO: alter files
      # next 'filename in filesToBeAdded'
      fn << filename
      return
    end
  end
  # if loop exited normally, create a new segment
  group << [filename]
end

# main
files = Hash.new { [] }
for filename in filesToBeAdded
  filesize=File.filesize(filename)
  addToGroup( files[ filesize ] )
end

> So questions in general:
> How can I alter items in a hash nicely?

hash[ key ].<any_method_you_like>

> Can I exit more loops with next/last/redo? (like in perl)

As others pointed out not in all versions of ruby.

> Is there something similar to python's for .. else ... structure? (Do
> something, ONLY when the loop is terminated normally (without break)

Dunno.

    robert