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Re^3: Rewrite Program Using Arrays

by aaron_baugher (Deacon)
on Mar 26, 2012 at 00:35 UTC ( #961560=note: print w/ replies, xml ) Need Help??


in reply to Re^2: Rewrite Program Using Arrays
in thread Rewrite Program Using Arrays

Well, you could get rid of your loop by using map, but my benchmark shows no gain there. Eliminating some intermediate variables does speed things up, though. If you get rid of @words and $word completely, you'll gain some time, regardless of which looping method you use:

#!/usr/bin/env perl use Modern::Perl; use Benchmark qw(:all); # create a line with words and spaces to split on my $line = ''; $line .= ('a', 'b', 'c', 'd', ' ')[rand(5)] for (1..1000); cmpthese( 100000, { 'loop with vars' => \&loopwithvars, 'loop sans vars' => \&loopsansvars, 'with map' => \&withmap, }); sub loopwithvars { my %wordcount; my @words = split ' ', $line; for my $word (@words){ $wordcount{$word}++; } } sub loopsansvars { my %wordcount; for (split ' ', $line){ $wordcount{$_}++; } } sub withmap { my %wordcount; map { $wordcount{$_}++ } split ' ', $line; } ###### results ###### Rate loop with vars with map loop sans vars loop with vars 11338/s -- -15% -17% with map 13369/s 18% -- -2% loop sans vars 13624/s 20% 2% --

Aaron B.
My Woefully Neglected Blog, where I occasionally mention Perl.


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Re^4: Rewrite Program Using Arrays
by ikegami (Pope) on Mar 27, 2012 at 20:54 UTC

    Get rid of a scope, use preinc instead of postinc.

    sub ikegami { my %wordcount; ++$wordcount{$_} for split ' ', $line; }
                      Rate loop with vars      with map loop sans vars       ikegami
    loop with vars  8324/s             --          -19%           -20%          -22%
    with map       10241/s            23%            --            -1%           -4%
    loop sans vars 10370/s            25%            1%             --           -3%
    ikegami        10666/s            28%            4%             3%            --
    

    (Post-increment in void context is optimised to pre-increment, but it's not in void context in "with map".)

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