Why is "Types of queries..." under "conditions"? Surely that's a feature?

I (we?) have no idea what you have, what you want, or where you need to get to.

Example: Heterogenic string:

ababababababaab
[download]

Homogenic string (after BWT (ref: Perl impl of bwt))

bbbbbbbaaaaaaaa
[download]

same characters stick together! I have not added any extra information to the initial string and yet have an encoder that homogenizes the initial string. So what other transforms you now of, that can be used to achieve similar behaviour

To what end?

and please provide links to acronyms, like BWT = Burrows-Wheeler_transform

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}

PS: Sorry, but "Problems with strings" is a lousy title.

Please read

• How do I compose an effective node title?
• How do I post a question effectively?
• Try To Make Sense

What is the character on i-th position of the original string. where 0<=i<=l.

I would have said this would be substr, except that i (0-based character position index(?)) may equal l (length of string(?)); I don't understand the last bit.

BWT = Burrows-Wheeler_transform is a way to provide lossless compression by using the redundancy of repeated passages (like syllables in speech)

My guess is the OP is still trying to defy entropy and to improve the compression of his last problem.

Cheers Rolf
_{(addicted to the Perl Programming Language :)
Wikisyntax for the Monastery FootballPerl is like chess, only without the dice}

Hello baxy77bax,

If I understand correctly your question and desired output one possible way is:

Regarding your second question on how to repeat the process for multiple strings (simply concatenate the strings):

Update: Last part (replace character in a string):

Hope this helps, Thanos.

I'm not at all sure I understand your requirement. The query you mention suggests that the easiest thing to do would be to keep the original string along with any transformations. Here's my stab at it.

use 5.026;
use warnings;

use Data::Dumper;

my @strings = qw{
   aaaaaaaaabababacbbbbbbbaccaabc
   aaaaaaaaaaaaaaaaacbbbbbbbaaaca
   aaaaaaaaabaaaaabbaaaaabaaccccc
   };

homogenise( \ @strings );
print Data::Dumper->Dumpxs( [ \ @strings ], [ qw{ *strings } ] );

sub homogenise
{
    my $raStrings = shift;
    my $len       = length $raStrings->[ 0 ];

    foreach my $string ( @{ $raStrings } )
    {
        $string = { original => $string };
        $string->{ byLine } =
           join q{},
           sort split m{}, $string->{ original };
    }

    my $allSorted =
       join q{},
       sort map { split m{}, $_->{ original } } @{ $raStrings };
    my $idx = 0;
    $raStrings->[ $idx ++ ]->{ bySet } = $_
       for unpack qq{(a$len)*}, $allSorted;
}
[download]

The output.

@strings = (
             {
               'bySet' => 'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaa',
               'original' => 'aaaaaaaaabababacbbbbbbbaccaabc',
               'byLine' => 'aaaaaaaaaaaaaaabbbbbbbbbbbcccc'
             },
             {
               'byLine' => 'aaaaaaaaaaaaaaaaaaaaabbbbbbbcc',
               'original' => 'aaaaaaaaaaaaaaaaacbbbbbbbaaaca',
               'bySet' => 'aaaaaaaaaaaaaaaaaaaaaaaaaaabbb'
             },
             {
               'byLine' => 'aaaaaaaaaaaaaaaaaaaaabbbbccccc',
               'bySet' => 'bbbbbbbbbbbbbbbbbbbccccccccccc',
               'original' => 'aaaaaaaaabaaaaabbaaaaabaaccccc'
             }
           );
[download]

I hope that this is vaguely in the direction you are wanting to go.