$VAR1 = {
          '010' => {
                     'Gross' => '15',
                     'name' => 'Moe',
                     'widget-2' => {
                                     'Gross' => '15',
                                     'Qty' => '1'
                                   },
                     'qty' => '1'
                   },
          '020' => {
                     'Gross' => '35',
                     'name' => 'Larry',
                     'widget-1' => {
                                     'Gross' => '15',
                                     'Qty' => '1'
                                   },
                     'widget-2' => {
                                     'Gross' => '20',
                                     'Qty' => '2'
                                   },
                     'qty' => '3'
                   }
        };

##</code><code>##

# perl
# http://www.perlmonks.org/?node_id=859450

use strict;
use warnings;
use diagnostics;
use 5.010;

use Data::Dumper;


my %input;

my $line = <DATA>; # skip 1st line

while ( my $line = <DATA> ) {
    chomp $line;
    my  ($tx, $name, $type, $product, $qty, $gross) = split /\s*,\s*/, $line;
    #say "$tx, $name, $type, $product, $qty, $gross";
    if ( $type eq 'Cart') {
        #say 'process Cart line';
        #say "data is $tx, $name, $qty, $gross";
             $input{$tx} = {
                                'name' => $name,
                                'qty'  => $qty,
                                'Gross'=> $gross,
                            }
    }
    elsif ( $type eq 'Item' ) {
        #say 'process Item line';
        #say "data is $tx, $name, $qty, $gross";
            $input{$tx} =   {
                                %{$input{$tx}},
                                $product => {
                                'Qty'        => $qty,
                                'Gross'      => $gross,
                                },
            }
                
    }
    else {
        warn 'line not recognized';
    }
    
}

#say Dumper(\%input);

my @items = qw( widget-1 widget-2); # all available items, need to be defined in advance to have a stable order of output items

say 'Txn ID,  Name ,  Qty, Gross, widget-1 Qty, widget-1 Gross, widget-2 Qty, widget-2 Gross';
foreach my $tx (keys %input) {
    #say "prcess transaction $tx";
    my $lineout = "$tx, $input{$tx}{'name'}, $input{$tx}{'qty'},$input{$tx}{'Gross'}, ";
    foreach my $item ( @items ) {
        #say "found key $key";
        #say "found data $input{$tx}{$key}";
            #say "process item $input{$tx}{$item}";
            $lineout .= ", ";
            $lineout .= $input{$tx}{$item}{'Qty'} // '';
            $lineout .= ", ";
            $lineout .= $input{$tx}{$item}{'Gross'} // '';
    }
    say $lineout;
}

__DATA__
Txn ID,  Name ,  Type , Product ID, Qty, Gross
010   ,  Moe  ,  Cart ,           ,  1 ,   15
010   ,  Moe  ,  Item ,  widget-2 ,  1 ,   15
020   ,  Larry,  Cart ,           ,  3 ,   35
020   ,  Larry,  Item ,  widget-1 ,  1 ,   15
020   ,  Larry,  Item ,  widget-2 ,  2 ,   20

##</code><code>##

Txn ID,  Name ,  Qty, Gross, widget-1 Qty, widget-1 Gross, widget-2 Qty, widget-2 Gross
010, Moe, 1,15, , , , 1, 15
020, Larry, 3,35, , 1, 15, 2, 20