#! /usr/bin/perl -w

use strict;
use Benchmark qw/cmpthese/;

my %h;
my $nr = shift || 10000000;
$h{$nr} = ((rand() > 0.2) ? 1 : undef) while $nr--;

sub by_for {
    my $h = shift;
    my @def;
    $def[ defined $_ ? 1 : 0]++ for values %$h;
    @def;
}

sub by_grep {
    my $h = shift;
    (
        scalar (grep !defined, values %$h),
        scalar (grep  defined, values %$h),
    );
}

printf "by_for:  undefined=%d, defined=%d\n", by_for( \%h );
printf "by_grep: undefined=%d, defined=%d\n", by_grep( \%h );

cmpthese( -5, {
        for  => ' by_for( \%h ) ',
        grep => ' by_grep( \%h ) ',
    }
);