use Benchmark; my @list; for ( 0..9999 ) { push @list, sprintf "%d", 100 * rand ; } timethese( 1000, { 'keys_map' => sub { my @uniq = keys %{{ map {$_ => 1} @list }}; }, 'grep_seen' => sub { my %seen; my @uniq = grep ! $seen{$_}++, @list; }, } );