Re^2: Count and List Items in a List

[ikegami]

Except map is painfully slow in void context:

use strict;
use warnings;

use Benchmark qw( cmpthese );

my @list = map { '' . int(rand(100)) } 1..1000;

sub map_test {
   my %counts = ();
   map { ++$counts{$_} } @list;
   1;
}

sub foreach_test {
   my %counts = ();
   ++$counts{$_} for @list;
   1;
}

cmpthese(-3, {
   map     => \&map_test,
   foreach => \&foreach_test,
});

This is perl, v5.6.1 built for MSWin32-x86-multi-thread

          Rate     map foreach
map      953/s      --    -25%
foreach 1278/s     34%      --

This is perl, v5.8.0 built for MSWin32-x86-multi-thread

          Rate     map foreach
map     1705/s      --    -25%
foreach 2288/s     34%      --

This is perl, v5.8.0 built for i386-freebsd

          Rate     map foreach
map      847/s      --    -29%
foreach 1190/s     40%      --

This may have been fixed since.

[Tanktalus]

This is perl, v5.8.6 built for i686-linux

           Rate foreach     map
foreach 47168/s      --     -2%
map     48260/s      2%      --

That said, I always prefer code that does what it says and says what it does. To me, for/foreach evaluates code foreach element in a list, while map maps (or transforms) one list into another. If you want to iterate over a list, use for or foreach. If you want to transform from one list to another, use map.