From: w_a_x_man <w_a_x_man@...>
Date: 2010-07-09T00:15:03+09:00
Subject: Re: Regular expressions, capture repeated groups

On Jul 8, 6:20 am, Iain Barnett <iainsp...@gmail.com> wrote:
> I'm trying to emulate something I've done in .Net many moons ago, which is capture a named group, but not just once, get all it's repetitions and then be able to see all those repetitions. I think they call them GroupCollections in C#. This is the kind of code I'm trying to emulate with Ruby(1.9.1):
>
> using System;
> using System.Text.RegularExpressions;
>
> public class Test
> {
>
>     public static void Main ()
>     {
>
>         // Define a regular expression for repeated words.
>         Regex rx = new Regex(@"\b(?<word>\w+)\s+(\k<word>)\b",
>           RegexOptions.Compiled | RegexOptions.IgnoreCase);
>
>         // Define a test string.        
>         string text = "The the quick brown fox  fox jumped over the lazy dog dog.";
>
>         // Find matches.
>         MatchCollection matches = rx.Matches(text);
>
>         // Report the number of matches found.
>         Console.WriteLine("{0} matches found in:\n   {1}",
>                           matches.Count,
>                           text);
>
>         // Report on each match.
>         foreach (Match match in matches)
>         {
>             GroupCollection groups = match.Groups;
>             Console.WriteLine("'{0}' repeated at positions {1} and {2}",  
>                               groups["word"].Value,
>                               groups[0].Index,
>                               groups[1].Index);
>         }
>
>     }
>
> }
>
> // The example produces the following output to the console:
> //       3 matches found in:
> //          The the quick brown fox  fox jumped over the lazy dog dog.
> //       'The' repeated at positions 0 and 4
> //       'fox' repeated at positions 20 and 25
> //       'dog' repeated at positions 50 and 54
>
> For example, if I had the string "11 12" I could have a regex like
> /
>  (?<first> \d+ ) \s \g<first>
> /x
>  that captured "11" and then the repetition "12" and put them in an array (or some kind of collection) referenced by the name.
>
> I think my attempts to get this to work are better explanations. What I want is the result
> #<MatchData "11 12" first:["11", "12"]> or something like it. At the moment all my attempts end with the named capture only keeping the last match it made i.e. 12 with no mention of 11.
>
> I know I could do this a different way, perhaps with split or something, but I'd like to know if it's possible with just regex. I understand the Oniguruma engine is used now but I can't find any good docs for it.
>
> These are my attempts, $ is my prompt.
>
> $ md1 = /
>                 (?<first> \d+ )
>                 \s \g<first>
>             /x.match( "11 12" )
> #<MatchData "11 12" first:"12">
>
> $ md1[:first]
> "12"
>
> $ md1 = /
>                 (?<first> \d+ )
>                 (?: \s \g<first> )?
>         /x.match( "11 12" )
> #<MatchData "11 12" first:"12">
>
> $ md1[:first]
> "12"
>
> $ md1 = /
>                 (?<first> \d+ )
>                 (?: \s
>                         (?<second> \g<first> )
>                 )?
>         /x.match( "11 12" )
> #<MatchData "11 12" first:"12" second:"12">
>
> $ md1[:first]
> "12"
>
> $ md1[:second]
> "12"
>
> $ md1 = /
>         (?: (?<first> \d+ )\s* )+
>       /x.match( "11 12" )
> #<MatchData "11 12" first:"12">
>
> $ md1[:first]
> "12"
>
> Iain

"The the quick brown fox  fox jumped over the lazy dog dog.".
scan(/((\w+) +\2)/i){|x| puts "#{ x[0] } #{ $~.offset(0)[0]}"}
The the 0
fox  fox 20
dog dog 50