Hello!

You already has been provided with more than one way to do this, and I want to participate in this game too. Here's another way - just like you wanted - using map: 

use strict;

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_cost;
my $sum_damage;
my $sum_armor;

map { 
  $sum_damage += $weapons_ref->{$_}->{damage}; 
  $sum_cost += $weapons_ref->{$_}->{cost};
  $sum_armor += $weapons_ref->{$_}->{armor} 
} keys %{ $weapons_ref };

print join(' ',$sum_cost, $sum_damage, $sum_armor), '\n';

[download]
157 30 0

[download]

This code is a little bit specific, while I think we should move towards more general code, to make reusing it more simpler. Let's refactor it: 

use strict;
use Data::Dumper;

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_result;
my @sum_fields = qw/cost damage armor/;

map { 
  my $name = $_;
  map { $sum_result->{$_} += $weapons_ref->{$name}->{$_} } @sum_fields
} keys %{ $weapons_ref };

print Dumper($sum_result);

[download]
$VAR1 = {
          'armor' => 0,
          'cost' => 157,
          'damage' => 30
        };

[download]

Next step is to refactor this code to a function, which will receive a hash, an array of fields that we like to sum, and return a hash with sums.

In reply to Re: using ref to hash of hash effectively by alexander_lunev
in thread using ref to hash of hash effectively by kalee

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