Here's a quick program that does what you request. It doesn't do full CSV parsing (just splitting on commas), but I presume you don't need help with that (use a module). The output isn't lined up vertically either - but that shouldn't matter either I presume. 
#!/usr/bin/perl  
         
use 5.010;
            
use strict;
use warnings;
 
my %data;
my %seen;

while (<DATA>) {
    chomp;
    my ($id, $name, $type, $pid, $qty, $gross) = split /\s*,\s*/;
    given ($type) {
        when ('Item') {
            $data{$id,$name}{$type}{$pid}{qty} += $qty;
            $data{$id,$name}{$type}{$pid}{gross} += $gross;   
            $seen{$pid} = 1;
            next;
        }
        when ('Cart') {
            $data{$id,$name}{$type}{qty} = $qty;
            $data{$id,$name}{$type}{gross} = $gross;
        }
    }
}

my @pids = sort keys %seen;

print "Txn ID, Name, Qty, Gross";
print ", $_ Qty, $_ Gross" for @pids;
print "\n";

foreach my $ckey (sort keys %data) {
    my ($id, $name) = split $;, $ckey;
    print "$id, $name, ", $data{$ckey}{Cart}{qty} // "", ", ",
                          $data{$ckey}{Cart}{gross} // "";
    foreach my $pid (@pids) {
        print ", ", $data{$ckey}{Item}{$pid}{qty} // "", ", ",
                    $data{$ckey}{Item}{$pid}{gross} // "";
    }
    print "\n";
}
    
    
__DATA__
Txn ID,  Name ,  Type , Product ID, Qty, Gross
010   ,  Moe  ,  Cart ,           ,  1 ,   15
010   ,  Moe  ,  Item ,  widget-1 ,  1 ,   15
020   ,  Larry,  Cart ,           ,  3 ,   35
020   ,  Larry,  Item ,  widget-1 ,  1 ,   15
020   ,  Larry,  Item ,  widget-2 ,  2 ,   20

[download]
Output: 
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

[download]

In reply to Re: How to combine rows of a spreadsheet by JavaFan
in thread How to combine rows of a spreadsheet by wrinkles

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.