use strict;
use Data::Dumper;

my %stock;
while (<DATA>) {
  my ($qty,$model,$size) = split(',',$_);
  $stock{$model} = [0,0,0,0] unless (exists $stock{$model});
  $stock{$model}[0] = $qty if ($size =~ /sm/i);
  $stock{$model}[1] = $qty if ($size =~ /md/i);
  $stock{$model}[2] = $qty if ($size =~ /lg/i);
  $stock{$model}[3] = $qty if ($size =~ /xl/i);
}

print Dumper(\%stock);

__DATA__
224,128,MD,B,840197082997
0,128,LG,B,840197083000
0,128,XL,B,840197083017
0,12,SM,B,840197082997
15,12,LG,B,840197083000
0,12,XL,B,840197083017
32,8,SM,B,840197082997