Re^2: Is it possible to make reference to substrings and sort them?

[hdb]

If you can spare the memory to double your text, you can create references to all your rotations. Below I use the Schwartzian transform to create the references once, then sort them.

my $text2 = "$text$text";
my $bwt4 = join('', 
        map{substr($text, ($_ - 1), 1)} 
        map{ $_->[0] }
        sort{ ${$a->[1]} cmp ${$b->[1]} }
        map{ 
          [$_,\substr($text2,$_,$ntext)]
        } 0..$ntext-1
);
print "$text: $bwt4\n";

[Anonymous Monk]

Good call on doubling the string. Though the Schwartzian seems unnecessary here:

my $text2 = "$text$text";
my $tlen = length($text);
my $bwt7 = join('', 
        map{ substr($$_, -1) }
        sort{ $$a cmp $$b }
        map{ \substr($text2, $_, $tlen) } 0..$tlen-1
);
print "$text: $bwt7\n";

Intermediate array of references consumes more memory than an array of offsets would, I think, but is faster to sort. Something to test and benchmark...