my %table;

while (<DATA>) {
    chomp;
    my @line = split /,/;
    my $key = join ",", @line[1..3];
    if ( exists( $table{$key} )) {
        warn "oops -- duplicate key $key... is there a problem with that?\n";
        next;  # just in case there's a problem with that
    }
    $table{$key} = join ",", @line[4,5];
}
# later on, if you really need the individual columns from the
# hash key or the hash value, just use "split /,/" as needed

# <update>
# note that you can easily search for groups of hash keys:

my @root23keys = sort grep /^23,/, keys %table;
my @r23p34keys = sort grep /^23,34,/, keys %table;

# and so on... </update>


__DATA__
1,2,3,4,100,A
10,20,30,40,200,B
11,21,31,41,300,C
12,22,32,42,400,D
13,23,33,43,500,E
13,23,33,53,600,F
13,23,33,63,700,G
13,23,34,73,800,H
13,23,34,83,900,I
13,24,35,93,1000,J
13,24,36,103,1100,K