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

Hello,
Very simple question for you, i've had a look at previous posts and documentation but can't work out how to do this. I have no problems creating a big multidimensional hash, but accessing it is a whole other story. This is the structure I have created.

$urls{'network1'}{'id'}='whatever';
$urls{'network2'}{'id'}='whatever';
$urls{'network3'}{'id'}='whatever';

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I tried just looping through the keys of %urls, but then get stuck about how to access the values of the second level of the hash, i.e. the whatever bit. Any nice 

foreach my $key (keys %urls) {

}

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style solution would be perfect. Thanks, Tom

Replies are listed 'Best First'.
Re: accessing a hash of hashes
by monkey_boy (Priest) on Feb 15, 2005 at 11:59 UTC 

    use strict;

my %urls;

$urls{'networkid'}{'someidIdontknow'}='somevalue1';
$urls{'networkid2'}{'someidIdontknow2'}='somevalue2';
$urls{'networkid3'}{'someidIdontknow3'}='somevalue3';

foreach my $network (keys %urls) {
    foreach my $key (keys %{$urls{$network}}) {
        print "$network\t$key\t$urls{$network}{$key}\n";
    }
}

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    Im so sick of my Signature...
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Re: accessing a hash of hashes
by tomhukins (Curate) on Feb 15, 2005 at 11:34 UTC

    Take a look at Perl's perlreftut and perlref documentation.

    Each item in %urls contains a hash reference. To access this hash reference as a hash, use %$key. To access the value of a key directly from a hash reference, use the -> operator.

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Re: accessing a hash of hashes
by Thilosophy (Curate) on Feb 15, 2005 at 11:37 UTC 
    foreach my $key (keys %urls) {
  print $urls{$key}{id};
}

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[d/l]

      Thanks for the reply, that would work for my example, but I should have explained that I don't actually know the value of ID all the time, so infact my structure might look more like this: 

      $urls{'networkid'}{'someidIdontknow'}='somevalue1';
$urls{'networkid2'}{'someidIdontknow2'}='somevalue2';
$urls{'networkid3'}{'someidIdontknow3'}='somevalue3';

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      So unfortunately I can't access the value I don't know directly, but need a means to loop through all the values.

      From looking at the post above I now have this code but it doesn't work.

      foreach my $network (keys %urls) {
    foreach my $key (keys %$network) {
        print "$key<br/>";
    }
}

      [download]

      Any ideas where i'm going wrong? I know it's something to do with accessing the hashref.

      Cheers, Tom

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[select]
        foreach my $network (keys %urls) {
    foreach my $key (keys %{$urls{$network}}) {
        print "$key<br/>";
    }
}

        [download]
        or 
        foreach my $network (values %urls) {
    foreach my $key (keys %$network) {
        print "$key<br/>";
    }
}

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Re: accessing a hash of hashes
by holli (Abbot) on Feb 15, 2005 at 11:41 UTC 
    my %hash = ( foo => { bar => baz } );
print $hash{foo}{bar};

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    In you code, $key is equiv. with foo.


    holli, /regexed monk/
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