Automatic creation of hash elements

atemon has asked for the wisdom of the Perl Monks concerning the following question:

Hi,

The Code

foreach $FD_NAME ( 1 .. 10) {

        if( $FD_NAME eq $CATEGORY_DATA{$FD_NAME}{'FIELD_NAME'}) { # Th
+e if causing prob
           
           #Do my stuff
           
       }
       
} 

print keys %CATEGORY_DATA;
[download]

The problem.
In the above code, the hash %CATEGORY_DATA is a HOH and has some values. Let us say the %CATEGORY_DATA is as follows.

%CATEGORY_DATA = (
    1 => ( FIELD_NAME => 'id' ),
    4 => ( FIELD_NAME => 'name' ),
);
[download]

In the "if" if I check for keys 1 & 2 everything is Ok. But when $FD_NAME is 3 ( Or any value which is NOT a key in the hash ) it creates an element in the hash. i.e when I get keys of %CATEGORY_DATA, I am getting all the numbers 1 to 10 :( Is there a way to get only keys which has some values?

Cheers !

--VC

My Home

Comment on Automatic creation of hash elements Select or Download Code

Replies are listed 'Best First'.
Re: Automatic creation of hash elements by kyle (Abbot) on Dec 11, 2007 at 03:56 UTC
You can check if a key exists or is defined without creating it. You could insert that into your test like so: `if ( exists $CATEGORY_DATA{$FD_NAME} && $FD_NAME eq $CATEGORY_DATA{$FD_NAME}{'FIELD_NAME'} )` [download] You could also only loop over the keys of your hash in the first place. `foreach my $FD_NAME ( keys %CATEGORY_DATA )` [download]	[reply] [d/l] [select]
Re: Automatic creation of hash elements by NetWallah (Canon) on Dec 11, 2007 at 04:46 UTC
You have run into Autovivification. To avoid that, you can do something like: `for( grep {exists $CATEGORY_DATA{$_}} 1..10){ if( $FD_NAME eq $CATEGORY_DATA{$_}{FIELD_NAME}) { ... } }` [download] "As you get older three things happen. The first is your memory goes, and I can't remember the other two... " - Sir Norman Wisdom	[reply] [d/l]