Monks, I'm in need of a second pair of eyes. I have the following bit of code to try to sort on the cat_name field.

foreach my $category (sort { ($list->{$_}->{cat_name} cmp $list->{$_}-
+>{cat_name}) } keys %$list) {
  say $list->{$category}{cat_name};
}

[download]

I'm getting the following errors over and over:

Use of uninitialized value $_ in hash element at ./facebook.pl line 34
+.
Use of uninitialized value $_ in hash element at ./facebook.pl line 34
+.
Use of uninitialized value in string comparison (cmp) at ./facebook.pl
+ line 34.
Use of uninitialized value in string comparison (cmp) at ./facebook.pl
+ line 34.

[download]

These repeated errors are followed by a listing of the categories, but they are in random order and are not sorted alphabetically. I have no idea why I am getting unitialized value errors. Each element in the hash has a cat_name key with a value.

Here's a sample of the data I'm trying to sort:

$list = 
{
          '174972792548177' => {
                               'places' => [
                                             {
                                               '264651060353078' => {
                                                                    'n
+ame' => 'WHIP City Towing',
                                                                    'l
+ink' => 'https://www.facebook.com/WHIP-City-Towing-264651060353078/'
                                                                  }
                                             },
                                             {
                                               '177166582312074' => {
                                                                    'l
+ink' => 'https://www.facebook.com/Center-City-Service-177166582312074
+/',
                                                                    'n
+ame' => 'Center City Service'
                                                                  }
                                             },
                                             {
                                               '965119126910980' => {
                                                                    'l
+ink' => 'https://www.facebook.com/Michaels-Towing-965119126910980/',
                                                                    'n
+ame' => 'Michael\'s Towing'
                                                                  }
                                             }
                                           ],
                               'cat_name' => 'Towing Service'
                             },
          '199850580046875' => {
                               'cat_name' => 'Garage Door Services',
                               'places' => [
                                             {
                                               '233152426881482' => {
                                                                    'l
+ink' => 'https://www.facebook.com/413doors/',
                                                                    'n
+ame' => '413 Doors & Home Services'
                                                                  }
                                             },
                                             {
                                               '432129326916445' => {
                                                                    'l
+ink' => 'https://www.facebook.com/Jfcsbose/',
                                                                    'n
+ame' => 'Jfcsbose'
                                                                  }
                                             },
                                             {
                                               '471289059572856' => {
                                                                    'l
+ink' => 'https://www.facebook.com/Conte-Door-Service-Inc-471289059572
+856/',
                                                                    'n
+ame' => 'Conte Door Service, Inc.'
                                                                  }
                                             }
                                           ]
                             },
          '127806747288007' => {
                               'places' => [
                                             {
                                               '152911074751051' => {
                                                                    'l
+ink' => 'https://www.facebook.com/pages/Pioneer-Valley-Rider-Training
+/152911074751051',
                                                                    'n
+ame' => 'Pioneer Valley Rider Training'
                                                                  }
                                             }
                                           ],
                               'cat_name' => 'Traffic School'
                             },

};

[download]

$PM = "Perl Monk's";
$MCF = "Most Clueless Friar Abbot Bishop Pontiff Deacon Curate";
$nysus = $PM . ' ' . $MCF;
Click here if you love Perl Monks

In reply to Getting unexpected errors when trying to sort hash of hashes by nysus

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.