my $x;
$x->{foo};
print $x; # it's a hash!

##</code><code>##

my $x;
$x->[0];
print $x; # it's an array!

##</code><code>##

my $event;

while( <> ) {
    chomp;
    my ( $time, $lane, $factory, $event ) = split " ", $_;
    $event->{ $factory }{ $lane }{ $time } = $event;
}

##</code><code>##

my $event = {};

while( <> ) {
    chomp;
    my ( $time, $lane, $factory, $event ) = split " ", $_;

    $event->{ $factory } = {}
        if not exists $event->{ $factory };

    $event->{ $factory }{ $lane } = {}
        if not exists $event->{ $factory }{ $lane };

    $event->{ $factory }{ $lane }{ $time } = $event;
}