use List::Util qw( max );

my $max_spam_len = max map length, 'Spam:', @spam;
my $format = "%-${max_spam_len}s  %s\n";

printf($format, 'Spam:', 'Ham:');

my $max_idx = max $#spam, $#ham;
for my $i (0..$max_idx) {
   printf($format,
      $i <= $#spam ? $spam[$i] : '',
      $i <= $#ham  ? $ham[$i]  : '',
   );
}

##</code><code>##

use List::Util qw( max );

sub print_columns {
   my ($data) = @_;

   my @headers;
   my @columns;

   for (my $i = 0; $i < @$data; ) {
      push(@headers, $data->[$i++]);
      push(@columns, $data->[$i++]);
   }

   my @col_widths = map {
      max map length, $headers[$_], @{$columns[$_]}
   } 0..$#headers;
   my $format = join('  ', map "%-${_}s",   @col_widths) . "\n";
   my $sep    = join('  ', map { '-' x $_ } @col_widths) . "\n";

   printf($format, @headers);
   print($sep);

   my $max_idx = max map { $#$_ } @columns;
   for my $i (0..$max_idx) {
      printf($format, map { $i < @$_ ? $_->[$i] : '' } @columns);
   }
}

print_columns([
   Spam => \@spam,
   Ham  => \@ham,
]);