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Re^3: Just 1 line explanation

by mreece (Friar)
on Mar 19, 2007 at 17:06 UTC ( #605529=note: print w/replies, xml ) Need Help??


in reply to Re^2: Just 1 line explanation
in thread Just 1 line explanation

benchmarks are funny things. have i made a mistake here, or is grep faster than first in this case? the real win is factoring out the call to param():
use strict; use Benchmark qw(cmpthese); use List::Util; ## a 'reasonable' worst-case scenario? first of list of twenty .. my @display_files = qw( one two three four five six seven eight nine ten eleven twelve thi +rteen fourteen fifteen sixteen seventeen eighteen nineteen twenty ); sub param { 'one' } cmpthese( -2, { grep_param => sub { unless( grep { $_ eq param('select') } @display_files ) { 1; } + }, param_grep => sub { my $select = param('select'); unless( grep { $_ eq $select } @display_files ) { 1; } }, found => sub { my $select = param('select'); my $found; foreach (@display_files) { if ($_ eq $select) { $found = 1; last; } } unless ($found) { 1; } }, first => sub { my $select = param('select'); my $found = List::Util::first { $_ eq $select } @display_files +; unless ($found) { 1; } } });
produces:
               Rate grep_param      first param_grep      found
grep_param  47285/s         --       -69%       -81%       -92%
first      154996/s       228%         --       -36%       -73%
param_grep 244086/s       416%        57%         --       -57%
found      565517/s      1096%       265%       132%         --
interestingly, change sub param to return undef (to get a failing test) and i get:
               Rate grep_param      first      found param_grep
grep_param  81919/s         --       -18%       -61%       -68%
first       99685/s        22%         --       -52%       -61%
found      207714/s       154%       108%         --       -18%
param_grep 254449/s       211%       155%        22%         --
personally, i think grep is the clearest and most familiar idiom, and for a shortish list of @display_files the performance gains of using the for () { ... last; } aren't worth it, especially if the failure case is common.

Replies are listed 'Best First'.
Re^4: Just 1 line explanation
by Anno (Deacon) on Mar 19, 2007 at 17:51 UTC
    I ran your benchmarks with similar results. With (much) longer lists first does come up second, still beaten by found. The low overhead of found's direct loop seems hard to beat.

    Anno

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