my @a = (shuffle 1 .. $N)[ 0 .. $E ];
my @b = (shuffle 1 .. $N)[ 0 .. $E ];
my @c = (shuffle 1 .. $N)[ 0 .. $E ];
my @d = (shuffle 1 .. $N)[ 0 .. $E ];

##</code><code>##

my %comp;
$comp{ $_ }{a} = 'a' for @a;
$comp{ $_ }{b} = 'b' for @b;
$comp{ $_ }{c} = 'c' for @c;
$comp{ $_ }{d} = 'd' for @d;

##</code><code>##

print "     : a b c d\n--------------";

##</code><code>##

printf "%4s : %s\n", $_, 
    join ' ', map{ $_||'-' } @{ $comp{ $_ } }{ 'a'..'d' }
    for sort{$a<=>$b} keys %comp;

##</code><code>##

for sort{$a<=>$b} keys %comp;

##</code><code>##

@{ $comp{ $_ } }{ 'a'..'d' }

##</code><code>##

map{ $_||'-' }

##</code><code>##

join ' ',

##</code><code>##

printf "%4s : %s\n", $_, 

##</code><code>##

   6 : a b - d