Since the weapon names don't seem to matter, only their attributes, I think it's simpler to iterate over the values of the weapons hash per Cristoforo's approach. This works with map, but I think it's even simpler (and IMHO clearer) to use for-loops: 

Win8 Strawberry 5.8.9.5 (32)  Sun 12/27/2020  5:07:00
C:\@Work\Perl\monks
>perl -Mstrict -Mwarnings -l
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 {  # works
#     my $attrib = $_;
#     map { $sum_result->{$_} += $attrib->{$_} } @sum_fields
#     } values %$weapons_ref;

for my $hr_attrib (values %$weapons_ref) {
    $sum_result->{$_} += $hr_attrib->{$_} for @sum_fields;
    }

print Dumper $sum_result;
^Z
$VAR1 = {
          'cost' => 157,
          'damage' => 30,
          'armor' => 0
        };

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In reply to Re^2: using ref to hash of hash effectively by AnomalousMonk
in thread using ref to hash of hash effectively by kalee

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