Check if key exists in hash using value from another hash as hash name

Question

I'm getting a variable $breed back in a callback and I'm checking if I've seen it before, and if I haven't, storing it in %hash by doing the following:

    if (exists $hash{$breed}) {
    #exists
    } else {
    #add it
    $hash{$breed};
    }

Now, since I would like to keep track of these unique $breeds in separate hashes, I made another hash to keep new hash names

%hashnames =(cats => 'cathash',
            dogs => 'doghash');
my %cathash = ();
my %doghash = ();

Since I'm getting $species back from my callback as well, I know I can do a lookup to get the correct hash I should be adding $breed to by doing:

$hashnames {$species}

I would think something like the following would be okay, but it is not:

if (exists ${$hashnames {$species}}{$breed}){
#exists
}else{
#add it
${$hashnames {$species}}{$breed};
}

In reality, there are hundreds of species and breeds. Is this possible? Maybe I'm going about it all wrong? Thanks.

Answer 1

You can do a hash of hashes:

I am not sure how you are getting your data, but here is a possible example:

my @lol = (['cats', 'persian cat'], ['dogs', 'border collie'], ['cats', 'persian cat'], ['dogs', 'german shepherd']); #generating data
my (%cats, %dogs);
my %species = ('cats' => \%cats, 'dogs' => \%dogs);

for my $specie_breed(@lol) {
  my ($s, $b) = @{$specie_breed};
  $species{$s}->{$b}++;
}

print Dumper \%species;

Result:

$VAR1 = {
          'cats' => {
                      'persian cat' => 2
                    },
          'dogs' => {
                      'german shepherd' => 1,
                      'border collie' => 1
                    }
        };

Here is an example using arrays in a hash with skipping:

my @lol = (['cats', 'persian cat'], ['dogs', 'border collie'],
           ['cats', 'persian cat'], ['dogs', 'german shepherd'],
           ['cats', 'Siamese']); #generating data
my (@cats, @dogs);
my %species = ('cats' => \@cats, 'dogs' => \@dogs);

for my $specie_breed(@lol) {
  my ($s, $b) = @{$specie_breed};
  if(! grep(/$b/, @{$species{$s}})) {
    push @{$species{$s}}, $b;
 }
}

print Dumper \%species;

Result:

$VAR1 = {
          'dogs' => [
                      'border collie',
                      'german shepherd'
                    ],
          'cats' => [
                      'persian cat', #only adds it once
                      'Siamese'
                    ]
        };