From: "David A. Black" <dblack@...>
Date: 2004-08-18T05:02:33+09:00
Subject: Re: multiple regexp matches

Hi --

On Wed, 18 Aug 2004, Zach Dennis wrote:

> According to rdoc you are mistaken.
> 
> I also think you are mistaken:
> 
> #!/usr/bin/ruby
> t = "This is my 1 text"
> 
> re = /([^\s]*\s).*(\d)(\s.)/
> md = re.match( t );
> puts md.offset(0);
> puts ""
> puts md.offset( 1 );
> puts ""
> puts md.offset( 2 );
> puts ""
> puts md.offset( 3 );
> 
> 
> It returns the correct offsets of the matches. offset(0) being the whole 
> regex, offset(1) does the first subexpression, offset(2) does the second 
> subexpression. It works.

The problem is that Kevin wanted to scan a string more than once with
the same regex:

  str = "abc abc abc"
  re = /(\w+)/    # not /(\w+) (\w+) (\w+)/

re will scan against str three times.  The difficulty is getting hold
of the offsets of all the matches from all three times, in relation to
the total length of the string.  

Someone will probably post a simple or elegant solution; in the
meantime, here's mine:

  def find_offsets(str,re)
    offsets = []
    first = 0
    of = [0,0]

    loop do
      break unless m = re.match(str[first..-1])
      break if m.captures.empty?
      m.captures.each_with_index do |c,i|
	of = m.offset(i+1)
	res = [c, [of[0]+first, of[1]+first ]]
	yield res if block_given?
	offsets << res
      end
      first += of[0]
    end

    offsets
  end

  # Little test:

  str = '<span id="1"> <span>...</span> </span>'
  re = /(<(\/?)span>)/i

  puts str
  (str.size/9).times { print "0123456789" }
  puts; puts

  find_offsets(str,re).each do |capture, (start, stop)|
    puts "\"#{capture}\" starts at #{start}, ends at #{stop}"
  end

  # Output:
  <span id="1"> <span>...</span> </span>
  0123456789012345678901234567890123456789

  "<span>" starts at 14, ends at 20
  "" starts at 15, ends at 15
  "</span>" starts at 23, ends at 30
  "/" starts at 24, ends at 25
  "</span>" starts at 31, ends at 38
  "/" starts at 32, ends at 33


David

-- 
David A. Black
dblack@wobblini.net