use strict;
use warnings;

my @categories=qw/a b c/;
my @master;

#replace this line with a while statement+chomp+split
#foreach my $d(@data){
while (my $line = <DATA>) {
  chomp $line;
  my $d = [ split(m{,}, $line) ];

  my %h;
  foreach my $c(0 .. $#categories){
    my $val=$d->[$c];
    my $cat=$categories[$c];

    $h{$val}=$cat;
  }
  push @master, \%h;
}

__DATA__
1,2,3
4,5,6
7,8
10,11,12