From: Arun Kumar <arun.einstein@...>
Date: 2009-04-29T21:00:14+09:00
Subject: Re: Random Access using IO#pos in code blocks

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Thank you so much for the kind responses! I'm pleased to be part of such a
kind community :)

On Wed, Apr 29, 2009 at 4:32 PM, Robert Klemme
<shortcutter@googlemail.com>wrote:

> 2009/4/29 Brian Candler <b.candler@pobox.com>:
> > Unfortunately, I don't think string#scan will give you offsets into the
> > strings found.
> >
> > In ruby 1.8 you can write this:
> >
> >  pos =3D 0
> >  while md =3D /\b\w+\b/.match(para[pos..-1])
> >    word =3D md[0]
> >    puts "Match #{word} at #{para_pos+pos+md.begin(0)}"
> >    pos +=3D md.end(0)
> >    ...
> >  end
> >
> > In ruby 1.9 (but not 1.8.6/1.8.7), Regexp.match takes a start pos, so
> > you could optimise it to this:
> >
> >  pos =3D 0
> >  while md =3D /\b\w+\b/.match(para, pos)
> >    word =3D md[0]
> >    puts "Match #{word} at #{para_pos+md.begin(0)}"
> >    pos =3D md.end(0)
> >    ...
> >  end
>
> String#scan is likely faster than manually matching portions with
> #match.  In both versions of Ruby you can do this to get the
> /character/ offset:
>
> irb(main):001:0> s=3D%{foo bar baz}
> =3D> "foo bar baz"
> irb(main):002:0> s.scan(/\w+/) { p $`.length }
> 0
> 4
> 8
> =3D> "foo bar baz"
>
> > However in ruby 1.9 the offsets used will be in terms of number of
> > characters, not number of bytes. It would be up to you to convert this
> > back into byte offsets into the file, if that's what you're after.
>
> This is an important point to remember!
>
> Kind regards
>
> robert
>
> --
> remember.guy do |as, often| as.you_can - without end
> http://blog.rubybestpractices.com/
>
>


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