Re: Speed comparison of foreach vs grep + map

As Corion pointed out, the switch from !$_ to /0/ is overpowering the other differences and invalidating your test.

But other improvements can be made.

There's no reason to use an intermediate array in the latter snippet. This avoids the creation of 5 million scalars.

my @e =
   grep !$_,
      map $_ % 2,
         @c;
[download]

You could even eliminate the grep.

my @e =
   map $_ % 2 ? () : 0,
      @c;
[download]

Similar improvements can be made for the foreach version.

my @e;
for my $c ( @c ) {
   my $d = $c % 2;
   push @e, $d if !$d;
}
[download]

my @e;
for my $c ( @c ) {
   push @e, 0 if !( $c % 2 );
}
[download]

Finally, I'm curious how these compare:

my @e = ( 0 ) x grep !( $_ % 2 ), @c;
[download]

my @e; push @e, 0 for 1 .. grep !( $_ % 2 ), @c;
[download]

Comment on Re: Speed comparison of foreach vs grep + map Select or Download Code

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Re^2: Speed comparison of foreach vs grep + map by ikegami (Patriarch) on May 29, 2025 at 16:48 UTC
Benchmarks: `#!/usr/bin/perl use strict; use warnings; use Benchmark qw( cmpthese ); my @c = 1 .. 1_000_000; cmpthese( -3, { for => sub { my @e; for my $c ( @c ) { my $d = $c % 2; push @e, $d if !$d; } }, for2 => sub { my @e; for my $c ( @c ) { push @e, 0 if !( $c % 2 ); } }, map_grep => sub { my @e = grep !$_, map $_ % 2, @c; }, map => sub { my @e = map $_ % 2 ? () : 0, @c; }, grep_x => sub { my @e = ( 0 ) x grep !( $_ % 2 ), @c; }, grep_for => sub { my @e; push @e, 0 for 1 .. grep !( $_ % 2 ), @c; }, } );` [download] Rate map_grep for grep_for map for2 grep_x map_grep 10.6/s -- -27% -43% -47% -51% -54% for 14.6/s 38% -- -21% -27% -33% -36% grep_for 18.4/s 75% 27% -- -7% -15% -20% map 19.9/s 88% 36% 8% -- -9% -13% for2 21.7/s 106% 49% 18% 9% -- -5% grep_x 22.9/s 117% 57% 24% 15% 6% -- Rate map_grep for grep_for map for2 grep_x map_grep 12.2/s -- -16% -34% -40% -45% -49% for 14.6/s 20% -- -22% -29% -35% -39% grep_for 18.6/s 52% 27% -- -9% -17% -23% map 20.5/s 68% 40% 10% -- -8% -15% for2 22.4/s 83% 53% 20% 9% -- -7% grep_x 24.1/s 97% 65% 29% 17% 8% -- Rate map_grep for grep_for map for2 grep_x map_grep 12.1/s -- -19% -31% -36% -45% -49% for 14.8/s 23% -- -15% -21% -32% -37% grep_for 17.4/s 44% 17% -- -8% -21% -27% map 18.8/s 56% 27% 8% -- -14% -21% for2 21.9/s 82% 48% 26% 16% -- -8% grep_x 23.7/s 97% 60% 37% 26% 8% -- [download]	[reply] [d/l] [select]

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Re^2: Speed comparison of foreach vs grep + map
by ikegami (Patriarch) on May 29, 2025 at 16:48 UTC

Benchmarks:

#!/usr/bin/perl

use strict;
use warnings;

use Benchmark qw( cmpthese );

my @c = 1 .. 1_000_000;

cmpthese( -3, {
   for => sub {
      my @e;
      for my $c ( @c ) {
         my $d = $c % 2;
         push @e, $d if !$d;
      }
   },

   for2 => sub {
      my @e;
      for my $c ( @c ) {
         push @e, 0 if !( $c % 2 );
      }
   },

   map_grep => sub {
      my @e =
         grep !$_,
            map $_ % 2,
               @c;
   },

   map => sub {
      my @e =
         map $_ % 2 ? () : 0,
            @c;
   },

   grep_x => sub {
      my @e = ( 0 ) x grep !( $_ % 2 ), @c;
   },

   grep_for => sub {
      my @e; push @e, 0 for 1 .. grep !( $_ % 2 ), @c;
   },
} );
[download]

           Rate map_grep      for grep_for      map     for2   grep_x
map_grep 10.6/s       --     -27%     -43%     -47%     -51%     -54%
for      14.6/s      38%       --     -21%     -27%     -33%     -36%
grep_for 18.4/s      75%      27%       --      -7%     -15%     -20%
map      19.9/s      88%      36%       8%       --      -9%     -13%
for2     21.7/s     106%      49%      18%       9%       --      -5%
grep_x   22.9/s     117%      57%      24%      15%       6%       --

           Rate map_grep      for grep_for      map     for2   grep_x
map_grep 12.2/s       --     -16%     -34%     -40%     -45%     -49%
for      14.6/s      20%       --     -22%     -29%     -35%     -39%
grep_for 18.6/s      52%      27%       --      -9%     -17%     -23%
map      20.5/s      68%      40%      10%       --      -8%     -15%
for2     22.4/s      83%      53%      20%       9%       --      -7%
grep_x   24.1/s      97%      65%      29%      17%       8%       --

           Rate map_grep      for grep_for      map     for2   grep_x
map_grep 12.1/s       --     -19%     -31%     -36%     -45%     -49%
for      14.8/s      23%       --     -15%     -21%     -32%     -37%
grep_for 17.4/s      44%      17%       --      -8%     -21%     -27%
map      18.8/s      56%      27%       8%       --     -14%     -21%
for2     21.9/s      82%      48%      26%      16%       --      -8%
grep_x   23.7/s      97%      60%      37%      26%       8%       --
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