my @order = ();
  my %values;

  while (<IN>)
  {
    my ($col1, $col2) = split;
    push @order, $col1 unless exists $values{$col1};
    push @{$values{$col1}}, $col2
  }

  # and now print it:
  foreach my $col1 (@order) {
  {
    print join("\t", $col1, @{$values{$col1}}), "\n";
  }