Re: Re: Perl Idioms Explained - keys %{{map{$_=>1}@list}}

[LanceDeeply]

This is the way I've usually seen it done. I was curious, so I ran a benchmark against the two.

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; },
    }
);

Yields the following output.

Benchmark: timing 1000 iterations of grep_seen, keys_map...
 grep_seen: 13 wallclock secs (11.17 usr +  0.00 sys = 11.17 CPU) @ 89
+.52/s (n=1000)
  keys_map: 30 wallclock secs (29.28 usr +  0.00 sys = 29.28 CPU) @ 34
+.15/s (n=1000)

[RMGir]

Adding

'keys_map_undef' => sub { my @uniq = keys %{{ map {$_ => undef} @list 
+}}; },

to test the undef suggestion, it turns out to be 15-20% faster than using 1.

grep still wins, though.
--
Mike