sub remove_from_dtgs {
    my ($dtg,$file) = @_;
    for my $i (reverse 0 .. $#files) {
        splice @{$dtgs{$dtg}}, $i, 1 if $dtgs{$dtg}[$i] eq $file;
    }
    delete $dtgs{$dtg} unless @{$dtgs{$dtg}};
}

##</code><code>##

sub remove_from_dtgs {
    my ($dtg,$file) = @_;
    for my $i (reverse 0 .. $#files) {
        if ($dtgs{$dtg}[$i] eq $file) {
            splice @{$dtgs{$dtg}}, $i, 1;
            delete $dtgs{$dtg} unless @{$dtgs{$dtg}};
            last;
        }
    }
}

##</code><code>##

open(my $dtg_file, "<", $infile) or die "Unable to open $infile: $!\n";
while(<$dtg_file>) {
    chomp;
    my ($dtg,@files) = split /:/;
    $dtgs{$dtg}{$_}++ for @files;
}
close $dtg_file;

sub remove_from_dtgs {
    my ($dtg,$file) = @_;
    delete $dtgs{$dtg}{$file};
    delete $dtgs{$dtg} if !keys %{$dtgs{$dtg}}
}