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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)

In reply to Re: Re: Perl Idioms Explained - keys %{{map{$_=>1}@list}} by LanceDeeply
in thread Perl Idioms Explained - keys %{{map{$_=>1}@list}} by broquaint

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