# Rebuild the canonical list, but now we lose duplicates
foreach my $name (keys %byname) {
    # First instance of the id number needs an array ref
    if (! $final{$byname{$name}}) {
	$final{$byname{$name}} = [ $name ];
    }
    # Additional instances get pushed onto the existing
    # (anonymous) array
    else {
	push @{$final{$byname{$name}}}, $name;
    }
}