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

Dear experts:

I have a reference to a hash-of-hashes and need to delete from it. Deleting a leaf node is no problem: 
   delete ($HoHref->{$element}{$attr});

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but deleting an entire element does nothing and returns no warning or error: 
   delete ($HoHref->{$element});

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I don't think the leaf nodes have to be removed first, but in trying to do so, I found that this does nothing either: 
   $HoHref->{$element} = ();

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Any clues would be most welcome! Thanks in advance,

Stephen

Janitored by Arunbear - replaced pre tags with code tags, to allow code extraction

Replies are listed 'Best First'.
Re: delete from HoH ref
by dave_the_m (Monsignor) on Apr 10, 2005 at 14:39 UTC
    Works for me: 
    $ cat /tmp/p
my $HoHref = { a => { p => 1 }, b => { q => 1 } };
use Data::Dumper;
print Dumper $HoHref;
delete $HoHref->{a};
print Dumper $HoHref;
$
$ perl /tmp/p
$VAR1 = {
          'a' => {
                   'p' => 1
                 },
          'b' => {
                   'q' => 1
                 }
        };
$VAR1 = {
          'b' => {
                   'q' => 1
                 }
        };

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    You'll need to give more details, such as a small (but complete) sample script, for us to help you further.

    Dave.

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[d/l]
      Thanks for the reply. I looked harder at my code and realized the delete was working but I had a control-flow problem!

      Thank you, Stephen
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Re: delete from HoH ref
by holli (Abbot) on Apr 10, 2005 at 14:40 UTC 
    use strict;
use warnings;

use Data::Dumper;

my $h =
{
    a => { c=>"b" },
    A => { C=>"B" },
};

delete $h->{a}{c};
delete $h->{A};

print Dumper ($h);

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    prints 
    $VAR1 = {
          'a' => {}
        };

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    as expected. You might want to show us some of your code.


    holli, /regexed monk/
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Re: delete from HoH ref
by borisz (Canon) on Apr 10, 2005 at 14:45 UTC 
    delete ($HoHref->{$element});

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    should work as expected. 
    use Data::Dumper;
my $href = {
             elem1 => { attr => 12, attr2 => 44 },
             elem2 => { attr => 12, attr2 => 44 }
};
delete $href->{elem1};
print Dumper($href);
__OUTPUT__
$VAR1 = {
          'elem2' => {
                       'attr2' => 44,
                       'attr' => 12
                     }
        };

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    Boris
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Re: delete from HoH ref
by Zaxo (Archbishop) on Apr 10, 2005 at 14:42 UTC

    Are you sure $element is a key in %$HoHref ? What you're doing does work: 

    $ perl -e'my $hohr = {foo=>{},bar=>{},baz=>{}};print delete ($hohr->{b
+az}), $/;print keys %$hohr'
HASH(0x804b5c0)
barfoo$

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    Perhaps you have unchomped newlines in your keys or $element? That could explain why your keys aren't found.

    After Compline,
    Zaxo

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Re: delete from HoH ref
by sh1tn (Priest) on Apr 10, 2005 at 14:44 UTC
    Please, show the output of: 
    use Data::Dumper;
print Dumper($HoHref);

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[d/l]
      Before *and* after the delete, preferably.
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