use strict;
use warnings;
use Benchmark qw(cmpthese);
use List::MoreUtils;

my @data;                                   # AB
for ( 1 .. 1e4 ) {
    push @data, int( rand 1e6 );
}

my @lines;                                  # BU
for ( 1 .. 1e3 ) {
    my $line = int( rand 1e6 );
    $line .= chr(9) . int( rand 1e6 ) while length( $line ) < 4096;
    push @lines, $line;
}

my @values = map {int rand 10} 1 .. 1000;   # GF

my $data;
$data = \@data;
#$data = \@lines;
#$data = \@values;

sub uniq1 {  # copied from List::MoreUtils
    my %h;
    map { $h{$_}++ == 0 ? $_ : () } @_;
}

sub uniq2 {
    my %h;
    grep { $h{$_}++ == 0 } @_;
}

sub uniq3 {  # OP
    my %h;
    grep {$h{$_} = undef} @_;
    keys %h;
}

sub uniq4 {  # BrowserUk
    my %h;
    undef @h{ @_ };
    keys %h;
}

cmpthese(-1, {
    'uniqM'  => sub { my @uniq = List::MoreUtils::uniq(@$data) },
    'uniq1'  => sub { my @uniq = uniq1(@$data) },
    'uniq2'  => sub { my @uniq = uniq2(@$data) },
    'uniq3'  => sub { my @uniq = uniq3(@$data) },
    'uniq4'  => sub { my @uniq = uniq4(@$data) },
});

##</code><code>##

        Rate uniq1 uniqM uniq2 uniq3 uniq4
uniq1 35.2/s    --   -1%   -5%  -15%  -21%
uniqM 35.5/s    1%    --   -4%  -14%  -20%
uniq2 36.9/s    5%    4%    --  -11%  -17%
uniq3 41.5/s   18%   17%   13%    --   -7%
uniq4 44.7/s   27%   26%   21%    8%    --

##</code><code>##

        Rate uniq2 uniq1 uniq3 uniq4
uniq2 34.2/s    --   -4%  -30%  -30%
uniq1 35.5/s    4%    --  -28%  -28%
uniq3 49.1/s   43%   38%    --    0%
uniq4 49.1/s   43%   38%    0%    --

##</code><code>##

        Rate uniqM uniq2 uniq1 uniq3 uniq4
uniqM 24.8/s    --  -28%  -30%  -50%  -50%
uniq2 34.2/s   38%    --   -4%  -31%  -31%
uniq1 35.5/s   43%    4%    --  -28%  -28%
uniq3 49.5/s  100%   45%   39%    --    0%
uniq4 49.5/s  100%   45%   39%    0%    --

##</code><code>##

         Rate uniq1 uniq2 uniq3 uniq4 uniqM
uniq1  3445/s    --  -18%  -27%  -77%  -80%
uniq2  4213/s   22%    --  -10%  -72%  -75%
uniq3  4696/s   36%   11%    --  -69%  -72%
uniq4 15175/s  340%  260%  223%    --  -10%
uniqM 16905/s  391%  301%  260%   11%    --