use strict;
use warnings;

my $IDX_ID = 0;
my $IDX_NAME = 1;
my $IDX_ITEM = 2;
my $IDX_DESC = 3;
my $IDX_PRICE = 4;

#-------------------------------------------------
# read lines into an *array of an array references*
#--------------------------------------------------

my @aLines;
while (my $line = <DATA>) {
  #get rid of trailing new line
  chomp $line;

  # break into columns
  # Note: I've used a simple split to populate columns,
  #       since I don't have Text::CVS_XS on my system
  my @aColumns = split( /\s*,\s*/, $line);

  #convert @aColumns to a reference and add it to
  #the end of the array
  # Note: this part is the same, no matter whether you use
  #       split or Text::CVS_XS

  push @aLines, \@aColumns;
}

#-------------------------------------------------
# sort the lines on id
#--------------------------------------------------

# {...} is an anonymous subroutine used for sorting
# it has two special implicit parameters $a, $b, each
# representing two elements of @aLines, i.e. two different
# array references.  These array references are just
# columns and we want to compare id's.
#
# Since these are references to arrays rather than arrays
# we use $a->[...] instead of $a[...]

my @aSorted = sort { $a->[$IDX_ID] < $b->[$IDX_ID] } @aLines;

#-------------------------------------------------
# now group and print
#--------------------------------------------------

my $currentId;

for my $aColumns (@aSorted) {
  my $id = $aColumns->[$IDX_ID];
  my $name = $aColumns->[$IDX_NAME];
  my $itemId = $aColumns->[$IDX_ITEM];
  my $itemDesc = $aColumns->[$IDX_DESC];
  my $price = $aColumns->[$IDX_PRICE];


  #do we have the start of new order?
  if (!defined($currentId) || ($id ne $currentId)) {
    #if we are finishing an order, close it before we begin
    #the next one.
    if (defined($currentId)) {
      print "</order>\n";
    }

    #set current id to new current id
    $currentId = $id;

    #print out order header XML
    print "<order>\n";
    print "  <order_id>$id</order_id>\n";
    print "  <name>$name</name>\n";
  }

  #print XML for item
  print "  <item>\n";
  print "    <item_id>$itemId</item_id>\n";
  print "    <item_desc>$itemDesc</item_desc>\n";
  print "    <price>$price</price>\n";
  print "  </item>\n";
}

#close final order
if (defined($currentId)) {
  #we are finishing an order
  #close it before we begin next
  print "</order>\n";
}

__DATA__
1, bill smith, 11, red shoes, 39.99
2, john doe, 32, black hat, 21.59
3, jane lee, 12, green shoes, 29.99
2, john doe, 11, red shoes, 39.99