For what value of "does not work"? Could it be that deleting the city then revivfying it by "deleting" the (non-existant) ZIP field is causing you grief? Consider:

use strict;
use warnings;
use Data::Dump::Streamer;

my $location_hash = {
    'New York' => {ZIP => '123-456-789'},
    'Dunedin' => {ZIP => '9001'}
    };

for my $city ( keys %$location_hash ) {
    print "$city $location_hash->{ $city }->{ZIP}\n";

    delete ($location_hash->{ $city });
    delete ($location_hash->{ $city }->{ 'ZIP' } );
}

Dump $location_hash;
[download]

Prints:

Dunedin 9001
New York 123-456-789
$HASH1 = {
           Dunedin    => {},
           "New York" => {}
         };
[download]

You will note that the process of referencing the ZIP key in the second delete autovivifies the city key that you had just deleted. The first delete works and does everything required. The second delete is not required and is likely what is causing you confusion.

I had to remove the delete for deleting the category. I guess I was getting tired. Thanks

Maybe you'd better explain why you want to delete them?

Oh, good catch. I should not be deleting both inside of the inner loop! Thanks! I am trying to remove the values after processing because, I can possibly receive an error from this program and I need to know which cities I processed when the error occurred. So, I wont process the same cities again.
It appears that it will delete the zip code and state but not the city.

 
printf "Before deleting: city= %s state=%s zip= %s\n",
   $city ,
   $location_hash->{ $city }->{ 'ST' },
   $location_hash->{ $city }->{ 'ZIP' };

   delete ($location_hash->{ $city });
   delete ($location_hash->{ $city }->{ 'ST' }) ;
   delete ($location_hash->{ $city }->{ 'ZIP' }) ;

printf "After deleting: city= %s state=%s zip= %s\n",
   $city,
   $location_hash->{ $city }->{ 'ST' },
   $location_hash->{ $city }->{ 'ZIP' };
[download]


Output:



Before deleting: city= Lucketts state=VA zip= 20176
After deleting: city= Lucketts state= zip=
[download]

Ok, I feel like an idiot ... lol It kept printing $city because it was NOT in the hash. $city was declared above. I almost did not admit it but I wanted you all to get a good laugh :) new code:

for my $city ( keys %$location_hash ) {
   .
   .
   .

   printf "Before deleting: state=%s zip= %s\n",
      $location_hash->{ $city }->{ 'ST' },
      $location_hash->{ $city }->{ 'ZIP' };

   delete ($location_hash->{ $city });
   ### delete ($location_hash->{ $city }->{ 'ST' }) ;
   ### delete ($location_hash->{ $city }->{ 'ZIP' }) ;

   printf "After deleting: state=%s zip= %s\n",
      $location_hash->{ $city }->{ 'ST' },
      $location_hash->{ $city }->{ 'ZIP' };

} end for loop
[download]

Output:

Before deleting: state=VA zip= 20176
After deleting: state= zip=
Before deleting: state=VA zip= 20176
After deleting: state= zip=
[download]

Everyone, thanks for your help. Sometimes it helps to have someone to talk to about it and as you explain it you think, "Dah."

Just for your information:

   printf "After deleting: state=%s zip= %s\n",
      $location_hash->{ $city }->{ 'ST' },
      $location_hash->{ $city }->{ 'ZIP' };
[download]

This code will re-create the key $city} in %$location_hash. $location_hash->{$city} has to exists before it can look up ST and/or ZIP. (autovivication)

Another note: $location_hash->{$city}->{'ST'} is the same as: $location_hash->{$city}{'ST'} which is the same as: <code>$location_hash->{$city}{ST}

Isn't this the classic "operating on a {data structure} inside a loop that iterates through the elements of that {data structure}" problem?

How do you know it's not working? Are you checking after the loop finishes? Are you sure the loop is iterating over everything you think it is?

UPDATE: While I'd still like to know the answers to the questions above, I like GrandFather's tack better. I was not aware of/thinking about the autovivification issue. I had assumed that you originally tried the first delete only, and subsequently added the other delete statements as debugging tools.

Thanks for your help.

delete ($location_hash->{ $city }) ;
delete ($location_hash->{ $city }->{ 'ZIP' } );
[download]

you delete the $city key and immediately create it again with value being the reference to empty hash. In the argument of second delete you treat $location_hash-{$city} as hash reference and Perl is "clever enough" to create it for you. So you end up with new ($city => {}) pair in %{%location_hash}.

I personally dislike this automatic structures creation (it affects arrays also) and believe that decent and clearly read operation should not modify your data but raise an exception instead because you are treating undefined value as hash reference.

Nevertheless, it can be useful for you to know, that delete returns the value deleted

my $city_ref = delete ($location_hash->{$city});
delete($city_ref->{'ZIP'});
[download]