#! perl
use Modern::Perl;

package Person
{
    use Moose;
    use constant DURATION => 100;

    has use_duration => ( isa => 'Int', is => 'ro', default =>  1, );
    has frequency    => ( isa => 'Int', is => 'ro', default => 50, );
    has number       => ( isa => 'Int', is => 'rw', default =>  0, );

    sub need_to_go
    {
        my ($self) = @_;
        return rand(DURATION) + 1 <= $self->frequency;
    }
}

package Nation
{
    use Moose;

    has population => (
                          isa     => 'ArrayRef[Person]',
                          is      => 'ro',
                          traits  => ['Array'],
                          handles => { obtain => 'push', },
                      );

    sub cull
    {
        use List::MoreUtils qw(part);
        my ($self) = @_;
        my ($keep, $go) = part { $_->need_to_go } @{ $self->population };
        @{ $self->population } = @$keep;
    }

    sub display
    {
        use Data::Dump;
        my ($self, $msg) = @_;
        say "\n$msg\n";
        dd  $self;
    }
}

package main
{
    my $people    = Nation->new;
    my $people_nr = 25;

    for my $case (0 .. $people_nr)
    {
        my $person = Person->new;
        $person->number($case);
        $people->obtain($person);
    }

    $people->display('Before:');
    $people->cull;
    $people->display('After:');
}

##</code><code>##

14:06 >perl 516_SoPW.pl

Before:

bless({
  population => [
    bless({ frequency => 50, number => 0, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 1, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 2, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 3, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 4, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 5, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 6, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 7, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 8, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 9, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 10, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 11, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 12, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 13, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 14, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 15, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 16, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 17, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 18, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 19, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 20, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 21, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 22, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 23, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 24, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 25, use_duration => 1 }, "Person"),
  ],
}, "Nation")

After:

bless({
  population => [
    bless({ frequency => 50, number => 0, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 1, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 2, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 5, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 6, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 9, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 12, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 13, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 14, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 15, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 16, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 18, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 21, use_duration => 1 }, "Person"),
    bless({ frequency => 50, number => 22, use_duration => 1 }, "Person"),
  ],
}, "Nation")

14:06 >