On Fri, 30 Oct 2009, at 11:13:24, Philip Potter <philip.g.potter@gmail.com> wrote:

>2009/10/30 Mark Fowler <mark@twoshortplanks.com>:
> my $i;
> my @new = grep { $i = !$i } @old;
>
>Thinking about it further, this could be more readable as:
>
>my @new = grep { ++$i % 2 } @old;
>
>[idea stolen from pod for List::MoreUtils::part]
>
>Phil
>
>

In one step.
 my $bool = 0; # or 1
 my @selection = grep { $bool ^= 1 } @data;

 Torsten