foreach my $id (sort keys %test) {
   delete $test{13};
}

print(scalar keys %test, "\n");  # 2

##</code><code>##

@anon_list = sort keys %test;
foreach my $id (@anon_list) {
   print "$id :: $test{$id}\n";
   delete $test{13};
}

##</code><code>##

foreach my $id (sort keys %test) {
   next if not exist $test{$id};
   print "$id :: $test{$id}\n";
   delete $test{13};
}