use warnings;

my @data;

sub numeric_idx {
    my $val = shift;
    return ord($val) - ord('A');
}

while (<DATA>) {
    chomp;
    my ($x, $y, $v) = split /\t/;
    $data[numeric_idx($x)][numeric_idx($y)] = $v if defined $v;
}


__DATA__
A       A
B       A       1
C       A       3
C       B       2
D       A       2
D       B       4
D       C       3