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

by LanceDeeply (Chaplain)
on Aug 04, 2003 at 18:58 UTC ( #280762=note: print w/replies, xml ) Need Help??


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

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)

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Re: Re: Re: Perl Idioms Explained - keys %{{map{$_=>1}@list}}
by RMGir (Prior) on Aug 04, 2003 at 20:28 UTC
    Adding
    'keys_map_undef' => sub { my @uniq = keys %{{ map {$_ => undef} @list +}}; },
    to test the undef suggestion, it turns out to be 15-20% faster than using 1.

    grep still wins, though.
    --
    Mike

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