How to delete empty hash element

[stevio]

Using Data:umper module I can see an empty hash element, in this case $VAR1/$VAR2

$VAR1 = '';
$VAR2 = {};
$VAR3 = '5';
$VAR4 = '7';

etc

How do I check and remove empty hash elements? Do I use undef?

 

[KevinADC]

use the delete() function

http://perldoc.perl.org/functions/delete.html

------------------------------------------
- Kevin, perl coder unexceptional!

 

[stevio]

I've looked at the delete function, but can't work out how to search through a hash and delete empty key=>values

 

[prex1]

Your [tt]$VAR1,[/tt] etc are not hash elements, so I'm not sure to understand what you mean. Also you can have only a single empty key value in a hash, corresponding to the string of zero length [tt]''[/tt]. This is easy to delete with
[tt]for(keys%hash{delete$hash{$_}unless$_}[/tt]
Note however that this will also delete the key '0'!
I can't see at the moment a generalized method for detecting whether a hash value is 'empty' as you say, as it depends on what you mean by empty. This
[tt]for(keys%hash{delete$hash{$_}unless$hash{$_}}[/tt]
will delete all values corresponding to false, that is the undefined scalar, a string of zero length, the string (or number) '0' (though not the string '00') and possibly a few others. However if, as in your example, you have references to arrays or hashes with zero elements, these will not be deleted, in this case you should test against the number of elements in them. There are also a few other cases to consider: references to subs, possibly elements defined through constants, and...?

Franco

http://www.xcalcs.com

: Online engineering calculations

http://www.megamag.it

: Magnetic brakes for fun rides

http://www.levitans.com

: Air bearing pads

 

[stevio]

prex1, maybe my terminology and assumptions were wrong, but I thought that by using Data:umper and the result was

$VAR1 = '';
$VAR2 = {};

that this meant that the key=>value pair was empty or NULL or zero length as you call it.

Let me ask a diff question - what does the above tell you about a key->value pair?

 

[KevinADC]

use Data:umper like this:

print Dumper \%hash

or whatever your data is. Give it a reference to your data that way you can see the data structure.

------------------------------------------
- Kevin, perl coder unexceptional!

 

[prex1]

Never used that module, but I understand it is informative only, so you won't use it for changing your data (such as deleting a key-value pair).
Concerning your last example, if that is the output of [tt]print Dumper %hash;[/tt] , it tells you that [tt]%hash;[/tt] has one key-value pair in it: the key is the string of zero length and the value is a reference to a hash with zero key-value pairs in it.

Franco

http://www.xcalcs.com

: Online engineering calculations

http://www.megamag.it

: Magnetic brakes for fun rides

http://www.levitans.com

: Air bearing pads

 

[KevinADC]

This reproduces the output that stevio posted:

%hash = ( '' => {}, 5 => 7);
use Data::Dumper;
print Dumper %hash;

passing a reference to the data:

%hash = ( '' => {}, 5 => 7);
use Data::Dumper;
print Dumper \%hash;

outputs something a bit more useful:

$VAR1 = {
          '' => {},
          '5' => 7
        };

------------------------------------------
- Kevin, perl coder unexceptional!