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

I'm using the twittercounter API to try and graph my twitter stats from the XML file. Once I get the XML file I use the data structure returned from XML::Simple but can't seem to access the hash of hashes for followersperdat. Here is the hash snippet: 
          'growth_since_2w' => '16923',
          'followersperdate' => {
                                'date2009-09-03' => '17839',
                                'date2009-08-14' => '17309',
                                'date2009-07-11' => '15530',
                                'date2009-06-23' => '13116',
                                'date2009-09-05' => '17883',
                                'date2009-08-25' => '17668',
                                'date2009-08-12' => '17309',
                                'date2009-09-09' => '17883',
                                'date2009-08-09' => '16754',
                                'date2009-08-10' => '16754',
                                'date2009-06-26' => '13845',
                                'date2009-08-27' => '17668',
                                'date2009-08-24' => '17668',
                                'date2009-06-29' => '14294',
                                'date2009-08-22' => '17668',
                                'date2009-08-11' => '16754',
                                'date2009-08-18' => '17309',
                                'date2009-08-02' => '16579',
                                'date2009-08-01' => '16579',
                                'date2009-09-08' => '17883',
                                'date2009-08-28' => '17668',
                                'date2009-09-06' => '17883',
                                'date2009-06-16' => '10161',
                                'date2009-08-20' => '17668',
                                'date2009-08-05' => '16579',
                                'date2009-09-04' => '17839',
                                'date2009-08-16' => '17309',
                                'date2009-08-03' => '16579',
                                'date2009-06-21' => '12101',
                                'date2009-08-21' => '17668',
                                'date2009-09-02' => '17839',
                                'date2009-09-10' => '17883',
                                'date2009-08-30' => '17830',
                                'date2009-08-26' => '17668',
                                'date2009-08-23' => '17668',
                                'date2009-07-31' => '16468',
                                'date2009-08-15' => '17309',
                                'date2009-08-19' => '17668',
                                'date2009-06-17' => '10161',
                                'date2009-08-17' => '17309',
                                'date2009-08-06' => '16579',
                                'date2009-08-04' => '16579',
                                'date2009-08-29' => '17830',
                                'date2009-06-25' => '13116',
                                'date2009-08-31' => '17830',
                                'date2009-07-14' => '15530',
                                'date2009-07-08' => '14685',
                                'date2009-06-18' => '10807',
                                'date2009-09-07' => '17883',
                                'date2009-07-02' => '14685',
                                'date2009-06-24' => '13116',
                                'date2009-07-18' => '15586',
                                'date2009-07-05' => '14685',
                                'date2009-09-11' => '17883',
                                'date2009-06-22' => '12552',
                                'date2009-08-13' => '17309',
                                'date2009-09-01' => '17839',
                                'date2009-06-19' => '11401',
                                'date2009-06-20' => '11401'
                              },
          'tomorrow' => '18014',

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Here is my data structure I'm using: 
    my $data = $xml->XMLin( $my_xml_file );

    my %followers = $data->{followersperdate};

...

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basically I just need the contents of 'followersperdate' so I can sort the dates and then use the corresponding values to plot my graph. Any help would be greatly appreciated. Can someone point me in the right direction?

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Re: access hash of hashes?
by ikegami (Patriarch) on Sep 11, 2009 at 17:39 UTC

    Hashes (such as %$data) can only contains scalars for values. So $data->{followersperdate} can't possibly hold a hash as you believe. Note the curlies in the Data::Dumper output. It holds a reference to a hash. 

    my $followers = $data->{followersperdate};
for my $date ( keys %$followers ) {
    my $id = $followers->{$date};
    ...
}

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      Thanks, that was it :)
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Re: access hash of hashes?
by BioLion (Curate) on Sep 11, 2009 at 17:47 UTC

    Looks like you are not dereferencing the followers hash :

    my $followers = $data->{followersperdate}; ## just copy the reference 
+to the interesting part of the hash

** OR **

my %followers = %{ $data->{followersperdate} }; ## dereference the int
+eresting bit

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    See perlref for more details.

    Other than for clarity this doesn't make much sense though, because you alredy have the data in a not-too-complex HoH, but you might want to look at Tie::Hash::Sorted, or just create an array of the hash keys in sorted order :

    my @sorted_keys = 
  sort 
    { $data->{ followersperdate }->{ $b } 
      <=> 
    $data->{ followersperdate }->{ $a } } ## hi to lo on values
      keys %{ $data->{ followersperdate } }; ## again dereferencing as
+ above

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    Or you can directly access the contents this way, if you only need the sorted contents the once.
    HTH.

    Just a something something...
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