#$elements{$id} = \@words;
push @{ $elements{$id}->[$_] }, $words[$_] for 0 .. $#words;
#...
#print "key: $k, value: ".join(', ',@$v).".\n";
print "key: $k\n";
for my $i ( 0 .. $#{$v} ) {
    print "  col $i: ". join( ', ', @{ $v->[$i] } ) ."\n";
}