$VAR1 = [
          {
            'amount' => '58.80',
            'quantity' => '1',
            'product_listid' => '800000FA-1450218051',
            'id' => '3938716373870073',
            'customer_listid' => '8000024C-1450196328',
            'datetime' => '1309966331'
          },
          {
            'amount' => '1.34',
            'quantity' => '1',
            'product_listid' => '800000FC-1450218057',
            'id' => '3938716373870073',
            'customer_listid' => '8000024C-1450196328',
            'datetime' => '1309966331'
          },
          {
            'amount' => '2.14',
            'quantity' => '1',
            'product_listid' => '8000010C-1450218105',
            'id' => '2446438717782054',
            'customer_listid' => '80000245-1450196318',
            'datetime' => '1310146917'
          },
          {
            'amount' => '1.34',
            'quantity' => '1',
            'product_listid' => '800000FC-1450218057',
            'id' => '2446438717782054',
            'customer_listid' => '80000245-1450196318',
            'datetime' => '1310146917'
          }
        ];

##</code><code>##

[ $id1 => [ { $hashrefs_with_id1 } ... ]
  $id2 => [ { $hashrefs_with_id2 } ... ]
]

##</code><code>##

$VAR1 = {
          '2446438717782054' => {
                                  'amount' => '1.34',
                                  'quantity' => '1',
                                  'product_listid' => '800000FC-1450218057',
                                  'customer_listid' => '80000245-1450196318',
                                  'datetime' => '1310146917'
                                },
          '3938716373870073' => {
                                  'amount' => '1.34',
                                  'quantity' => '1',
                                  'product_listid' => '800000FC-1450218057',
                                  'customer_listid' => '8000024C-1450196328',
                                  'datetime' => '1309966331'
                                }
        };

##</code><code>##

my @row = $r->hashes; # produce flat format of arrays of hashrefs
my %row;
for my $row (@row) {
  push @{$row{$row->{id}}}, $row;
}
warn Dumper(\%row);