Re^4: using ref to hash of hash effectively

In terms of aesthetics, my feeling is "each to his own". I used to use map in void context. I have no problem reading code like that. I no longer use it, but for completely different reasons (see below).

The performance hit was resolved in 5.8.1 (see "perl581delta: Miscellaneous Enhancements"). If you're coding to 5.8.0 or earlier, you should avoid map in void context; otherwise, the performance issue is moot.

Quite a few years ago, I benchmarked map against for. I was surprised at how much faster for was. That's the reason I would now choose

for (keys %{ $weapons_ref }) {
    ...
}
[download]

over

map { 
    ... 
} keys %{ $weapons_ref };
[download]

See Benchmark and run your own tests if you want.

— Ken

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Re^5: using ref to hash of hash effectively by alexander_lunev (Pilgrim) on Dec 27, 2020 at 19:18 UTC
Thank you for this. I've done this benchmark: use strict; use Benchmark qw(:all); my $weapons_ref = { dagger => { cost => 8, damage => 4, armor => 0 }, shortsword => { cost => 10, damage => 5, armor => 0 }, warhammer => { cost => 25, damage => 6, armor => 0 }, longsword => { cost => 40, damage => 7, armor => 0 }, greataxe => { cost => 74, damage => 8, armor => 0 }, }; my @sum_fields = qw/cost damage armor/; my $count; cmpthese($count, { 'MapSub' => sub { my $sum_result; map { my $name = $_; map { $sum_result->{$_} += $weapons_ref->{$name}->{$_} } @sum_ +fields } keys %{ $weapons_ref }; }, 'ForSub' => sub { my $sum_result; foreach my $name (keys %{ $weapons_ref }) { foreach my $field (@sum_fields) { $sum_result->{$field} += $weapons_ref->{$name}->{$field}; } } }, }); [download] And here's result: `Rate MapSub ForSub MapSub 197098/s -- -33% ForSub 294627/s 49% --` [download] map is a bit slower, yes, but not critical. Anyway, thank you again, I will remember this if have to do code optimization.	[reply] [d/l] [select]

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Re^5: using ref to hash of hash effectively
by alexander_lunev (Pilgrim) on Dec 27, 2020 at 19:18 UTC

Thank you for this. I've done this benchmark:

use strict;
use Benchmark qw(:all);

my $weapons_ref = {
    dagger => { cost => 8, damage => 4, armor => 0 },
    shortsword => { cost => 10, damage => 5, armor => 0 },
    warhammer => { cost => 25, damage => 6, armor => 0 },
    longsword => { cost => 40, damage => 7, armor => 0 },
    greataxe => { cost => 74, damage => 8, armor => 0 },
  };

my @sum_fields = qw/cost damage armor/;
my $count;

cmpthese($count, {
    'MapSub' => sub {
      my $sum_result;
      map { 
        my $name = $_;
        map { $sum_result->{$_} += $weapons_ref->{$name}->{$_} } @sum_
+fields
      } keys %{ $weapons_ref };
    },
    'ForSub' => sub {
      my $sum_result;
      foreach my $name (keys %{ $weapons_ref }) { 
        foreach my $field (@sum_fields) {
         $sum_result->{$field} += $weapons_ref->{$name}->{$field};
       }
      } 
    },
});
[download]

And here's result:

           Rate MapSub ForSub
MapSub 197098/s     --   -33%
ForSub 294627/s    49%     --
[download]

map is a bit slower, yes, but not critical. Anyway, thank you again, I will remember this if have to do code optimization.

[reply]
[d/l]
[select]