use Benchmark; @a= (0..100,0..100); $mine = <<'CODE'; my %hash; @hash{$_}++ for @a; @a = keys %hash; CODE $yours1 = <<'CODE'; my %hash; @hash{@a} = (); @a = keys %hash; CODE $yours2 = <<'CODE'; my %hash; @hash{@a} = @a; @a = values %hash; CODE $his = <<'CODE'; my %hash; map { $hash{$_}=1 } @a; @a = keys %hash; CODE timethese ( 10000, { 'mine' => $mine, 'yours1' => $yours1, 'yours2' => $yours2, 'his' => $his } ); __END__ C:\>perl test.pl Benchmark: timing 10000 iterations of his, mine, yours1, yours2... his: 17 wallclock secs (17.03 usr + 0.00 sys = 17.03 CPU) @ 587.20/s (n=10000) mine: 15 wallclock secs (15.05 usr + 0.00 sys = 15.05 CPU) @ 664.45/s (n=10000) yours1: 12 wallclock secs (11.76 usr + 0.00 sys = 11.76 CPU) @ 850.34/s (n=10000) yours2: 15 wallclock secs (14.78 usr + 0.00 sys = 14.78 CPU) @ 676.59/s (n=10000) C:\>