Working with TMPL_LOOP means working with AoHs. This one shows how to change an AoH to add selected items out of an array.

#!/usr/bin/perl

use strict;
use warnings;

use Data::Dumper;

my $aoh = [
             {col => "col1", val => "val1"},
             {col => "col2", val => "val2"},
             {col => "col3", val => "val3"},
             {col => "col4", val => "val4"},
             {col => "col5", val => "val5"},
          ];

my @selected = (3, 4, 1);

for my $item (@selected) {
  ${aoh}->[$item]->{selected} = "selected";
}

print Dumper($aoh);
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Add_on: if you just want to see the selected ones you can use TMPL_IF inside your TMPL_LOOP.