I can see how to present the number of things in common, but this "number of things that are different" is causing me to stumble just a bit. Comparing a,b,c,d vs x,y,z: there is nothing in common (that number is zero) - what is the difference number? 4 or 3 or what?

Update:
To find the common things, one way is to set up 2 translation hash tables like below - these can be used in combination to achieve that goal, but I am still unsure about "what difference means".

#!/usr/bin/perl -w
use strict;
use Data::Dump qw(pp);

my %country_2_name;
my %name_2_country;

while (<DATA>)
{
   s/\s*$//;  # trim trailing spaces (also chomps)
   
   my ($name, $countries) = split(' ',$_,2);   
   my @these_countries = split(/,/,$countries); 
   
   $name_2_country{$name} = [@these_countries];
   
   foreach my $this_country (@these_countries)
   {
      push @{$country_2_name{$this_country}}, $name; 
   }   
}

pp \%country_2_name;
pp \%name_2_country;

=prints
{
  Amsterdam => ["Name4"],
  Canada    => ["Name1", "Name2", "Name3", "Name5"],
  China     => ["Name3"],
  HongKong  => ["Name3"],
  India     => ["Name2", "Name5"],
  Ireland   => ["Name4"],
  London    => ["Name4"],
  Portugal  => ["Name2"],
  USA       => ["Name1", "Name4", "Name5"],
  Yemen     => ["Name1"],
}
{
  Name1 => ["USA", "Canada", "Yemen"],
  Name2 => ["Canada", "Portugal", "India"],
  Name3 => ["China", "HongKong", "Canada"],
  Name4 => ["London", "Amsterdam", "Ireland", "USA"],
  Name5 => ["India", "USA", "Canada"],
}
=cut

__DATA__
Name1  USA,Canada,Yemen 
Name2  Canada,Portugal,India
Name3  China,HongKong,Canada
Name4  London,Amsterdam,Ireland,USA
Name5  India,USA,Canada
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