My thought regarding merging hashes would be to make the values into references to anonymous arrays. The following demonstrates a roughly hacked "merge" subroutine that takes references to hashes, grabs all unique keys, and then iterates over the keys to build an array containing values in all hashes. I'm sure someone else can come behind me to improve this :)

Incidentally, what I like about this solution is that you don't lose any data!

use strict;
use warnings;
use Data::Dumper;

my %first = ( one => 1,
              two => 2,
              three => 3 );

my %second = ( one => 'uno',
               two => 'dos',
               foo => 'bar' );
               
my %third = (  one => [ 'this', 'is', 'a', 'test' ],
               two => 'dos',
               foo => { bar => 'raise',
                        baz => 'test' } );

my %new_hash = merge( \%first, \%second, \%third );
print Dumper( \%new_hash );

sub merge {
    my @hashes = @_;
    my ( %merged_hash, %temp, @keys );

    # grab unique keys
    foreach my $hash ( @hashes ) {
        foreach my $key ( keys %$hash ) {
            push @keys, $key if ! $temp{ $key }++;
        }
    }
    my @vals;

    # build the array
    foreach my $key ( @keys ) {
        foreach my $hash ( @hashes ) {
            push @vals, $hash->{ $key } if exists $hash->{ $key };
        }
        $merged_hash{ $key } = [@vals];
        @vals = ();
    }
    return %merged_hash;
}
[download]

Output:

$VAR1 = {
          'one' => [
                     1,
                     'uno',
                     [
                       'this',
                       'is',
                       'a',
                       'test'
                     ]
                   ],
          'three' => [
                       3
                     ],
          'foo' => [
                     'bar',
                     {
                       'baz' => 'test',
                       'bar' => 'raise'
                     }
                   ],
          'two' => [
                     2,
                     'dos',
                     'dos'
                   ]
        };
[download]

Note that it even allows you to merge complex data structures. Of course, I haven't tested (or commented) this too thoroughly, so there is no warranty included.

This answers your question about merging hashes. Of course, to get the country count, simply merge the hashes and and count the keys.

Cheers,
Ovid

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