Well, it's not that difficult to do in a template (but alas, I've done this sort of things many times): 
use 5.020;
use warnings;
use Template;

my $data =
    [[ qw(1 2 A 4) ],
     [ qw(3 4 A 5) ],
     [ qw(5 5 B 2) ],
     [ qw(6 2 B 3) ],
     [ qw(1 2 C 2) ],
     [ qw(2 3 C 2) ],
     [ qw(1 3 C 1) ],
    ];

my $template = <<'EOT';
[% SET category = '';
   FOREACH line IN data;
     IF line.2 != category;
       GET line.2; "\n";
       category = line.2;
     END;
     GET line.join(" "); "\n";
   END;
%]
EOT

my $tt = Template->new;
$tt->process(\$template,{data => $data});

[download]
That said, if you're munging your data structure in Perl, then I'd suggest a different structure with a hash as the top level, and lists of lists inside: 
{ A => [[qw(1 2 A 4)],[qw(3 4 A 5)]],
  B => [[qw(5 5 B 2)],[qw(6 2 B 3)]],
  C => [[qw(1 2 C 2)],[qw(2 3 C 2)],[qw(1 3 C 1)]],
}

[download]
...which can then be processed with a different template. Note the extra sort which is required because hash entries come in random order. 
use 5.020;
use warnings;
use Template;

my $data =
    [[ qw(1 2 A 4) ],
     [ qw(3 4 A 5) ],
     [ qw(5 5 B 2) ],
     [ qw(6 2 B 3) ],
     [ qw(1 2 C 2) ],
     [ qw(2 3 C 2) ],
     [ qw(1 3 C 1) ],
    ];

my %munged;
for my $record (@$data) {
    no warnings "uninitialized";
    push @{$munged{$record->[2]}}, $record;
}

my $template = <<'EOT';
[% FOREACH category IN data.keys.sort;
     GET category; "\n";
     FOREACH record IN data.$category;
       GET record.join(" ");"\n";
     END;
   END;
%]
EOT

my $tt = Template->new;
$tt->process(\$template,{data => \%munged});

[download]

In reply to Re: Control break with Template::Toolkit by haj
in thread Control break with Template::Toolkit by betacentauri

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