Re: Re: Re: When would you choose foreach instead of map?

[eric256]

I don't know how to check for memory usage (rather than the blunt method of watching the task manager) but here are some speed tests. It appears from this test that they are very simlar in speed for this summing operation. For is the winner but i'm not sure its a noticable portion until you climb into the severl hundered thousand range.

use strict;
use warnings;

use Benchmark qw(:all) ;

my $to = 10_000;

cmpthese(-5,
    {
        'Map100k' => sub { my $sum = 0;
                   map { $sum += $_ } 
                   1 .. 100_000;
                 },
        'For100k' => sub { my $sum = 0;
                   $sum += $_ for 1 .. 100_000;
                 },

        'Map10k' => sub { my $sum = 0;
                   map { $sum += $_ } 
                   1 .. 10_000;
                 },
        'For10k' => sub { my $sum = 0;
                   $sum += $_ for 1 .. 10_000;
                 },

        'Map1k' => sub { my $sum = 0;
                   map { $sum += $_ } 
                   1 .. 1_000;
                 },
        'For1k' => sub { my $sum = 0;
                   $sum += $_ for 1 .. 1_000;
                 },
    });

__END__
          Rate Map100k For100k  Map10k  For10k   Map1k   For1k
Map100k 18.6/s      --    -19%    -90%    -92%    -99%    -99%
For100k 23.1/s     24%      --    -88%    -90%    -99%    -99%
Map10k   187/s    905%    709%      --    -22%    -91%    -92%
For10k   239/s   1182%    933%     28%      --    -89%    -90%
Map1k   2077/s  11052%   8880%   1009%    770%      --    -13%
For1k   2387/s  12715%  10219%   1175%    899%     15%      --

[Abigail-II]

Your benchmark isn't comparing for-block vs map. It's comparing the for statement modifier against map. Statements modifiers don't have the overhead of entering and leaving a scope. Of course, in this particular case, the clear winner is one that doesn't loop.

#!/usr/bin/perl

use strict;
use warnings;

use Benchmark qw /cmpthese/;

my $base = 1000;
foreach my $mult (1, 10, 100) {
    my $code;
    my $max     = $mult * $base;
    {
        no strict 'refs';
        @{"main::array$mult"} = 1 .. $max;
    }
    my $map_var = "\$sum${mult}map";
    my $for_var = "\$sum${mult}for";
    my $mod_var = "\$sum${mult}mod";
    my $exp_var = "\$sum${mult}exp";
    $code -> {"map${mult}k"} = "$map_var = 0;" .
                               "map {$map_var += \$_} \@array$mult";
    $code -> {"for${mult}k"} = "$for_var = 0;" .
                               "for (\@array$mult) {$for_var += \$_}";
    $code -> {"mod${mult}k"} = "$mod_var = 0;" .
                               "$mod_var += \$_ for \@array$mult";
    $code -> {"exp${mult}k"} = "$exp_var = $max * ($max + 1) / 2;";

    cmpthese -1 => $code;
    print "\n";
    
    no strict 'refs';
    die "Unequal\n" unless ${"sum${mult}map"} == ${"sum${mult}for"} &&
                           ${"sum${mult}mod"} == ${"sum${mult}exp"} &&
                           ${"sum${mult}map"} == ${"sum${mult}exp"};
     
}
    
__END__
           Rate   map1k   for1k   mod1k   exp1k
map1k    1305/s      --    -58%    -64%   -100%
for1k    3140/s    141%      --    -12%   -100%
mod1k    3589/s    175%     14%      --   -100%
exp1k 6859842/s 525617% 218353% 191047%      --

            Rate   map10k   for10k   mod10k   exp10k
map10k     123/s       --     -59%     -66%    -100%
for10k     299/s     144%       --     -16%    -100%
mod10k     356/s     190%      19%       --    -100%
exp10k 7021713/s 5717581% 2347785% 1970572%       --

             Rate   map100k   for100k   mod100k   exp100k
map100k    12.3/s        --      -60%      -64%     -100%
for100k    30.5/s      148%        --      -11%     -100%
mod100k    34.2/s      179%       12%        --     -100%
exp100k 5383313/s 43894609% 17663897% 15724842%        --

Abigail

[eric256]

Thanks for the info on for as a modifier. I thought it was just kinda a shortcut and that the compiler produced a normal for block out of it. Good info and i'm sure we all new that an equation to calculate the total would be better/faster/smarter. We weren't benchmarking the math just the means of looping.