in reply to group things?

This is related to run length encoding. A regular expression to perform RLE is (found at http://hpaste.org/1987): 
sub encode {
    (my $string = shift) =~s/((.)\2*)/$2 . (length $1) /eg;
    $string;
}

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Maybe you can modify this function to capture the beginning and ending positions of each run.

Update: Spoiler follows... 

sub group {
  my $x = shift;
  my $pos = 0;
  my @groups;
  $x =~ s{ ((.)\2*)
           (?{ push(@groups, [ substr($^N,0,1), $pos, $pos+length($^N)
+ ]);
             $pos+=length($^N) })
         }{}gx;
  \@groups;
}

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In Section Seekers of Perl Wisdom