use strict;
use warnings;

my %plates;

while (<DATA>) {
     chomp;
     next if ! /(\w+)\s+(\d+)/;
     
     ++$plates{$1}{$2};
}

for my $group (sort keys %plates) {
     print "$group ", join ', ', sort {$a<=> $b} keys %{$plates{$group}};
     print "\n";
}

__DATA__
ABC 334
NTR 557
ABC 442
FTE 442
HHR 443
NTR 554
ABC 123