my %hist;
while (<DATA>) {
  chomp;
  my ($col0, @element) = split;
  $hist{$col0}{$_}++ for @element;
};

##</code><code>##

my %seen = ();
for my $element (keys(%hist1), keys(%hist2)) {
    $seen{$element}++;
}
my @uniq = keys %seen;