#!/user/bin/perl -w
use strict;
use Data::Dump qw[pp];
$|=1;

my %hash;

print "** Example 1 ***\n"; #pretty normal thing to do
for my $set('A'..'B')
{
   my @array1 = map { int(rand(100)) }(1..2); 
   my @array2 = map { int(rand(100)) }(1..5); 
   
   $hash{$set} = [ [@array1], [@array2] ];
}  

pp \%hash;

print "** Example 2 ***\n"; #a pitfall here
for my $set('G'..'H')
{
   my @array1 = map { int(rand(100)) }(1..2); 
   my @array2 = map { int(rand(100)) }(1..5); 
   
   $hash{$set} = [ \@array1, \@array2 ];
}

pp \%hash;

print "** Example ***3\n"; #the wrong thing to do
my @x;
my @y;

for my $set('X'..'Y')
{
   @x = map { int(rand(100)) }(1..2); 
   @y = map { int(rand(100)) }(1..5); 
   
   $hash{$set} = [ \@x, \@y ];
}

pp \%hash;
__END__
** Example 1 ***
{
  A => [[45, 13], [77, 53, 52, 21, 23]],
  B => [[38, 27], [4, 59, 52, 4, 83]],
}
** Example 2 ***
{
  A => [[45, 13], [77, 53, 52, 21, 23]],
  B => [[38, 27], [4, 59, 52, 4, 83]],
  G => [[3, 35], [13, 58, 35, 76, 64]],
  H => [[26, 39], [34, 91, 99, 74, 97]],
}
** Example ***3
do {
  my $a = {
    A => [[45, 13], [77, 53, 52, 21, 23]],
    B => [[38, 27], [4, 59, 52, 4, 83]],
    G => [[3, 35], [13, 58, 35, 76, 64]],
    H => [[26, 39], [34, 91, 99, 74, 97]],
    X => [[31, 63], [72, 71, 10, 80, 76]],
    Y => ['fix', 'fix'],
  };
  $a->{Y}[0] = $a->{X}[0];
  $a->{Y}[1] = $a->{X}[1];
  $a;
}