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

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%      --
[download]

___________
Eric Hodges

Comment on Re: Re: Re: When would you choose foreach instead of map? Download Code

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Re: When would you choose foreach instead of map? by Abigail-II (Bishop) on May 21, 2004 at 11:19 UTC
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% -- [download] Abigail	[reply] [d/l]
Re: Re: When would you choose foreach instead of map? by eric256 (Parson) on May 21, 2004 at 15:02 UTC
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. ___________ Eric Hodges	[reply]