I have the following code abstract: 
use strict;

my %tables = (
  'Table_1' => {'Schema' => 'dbo'},
  'Table_2' => {'Schema' => 'dbo'}
);

my %fields = (
  'Table_1' => {
    'Field_1' => {'Datatype' => 'int', 'Position' => 1},
    'Field_2' => {'Datatype' => 'char', 'Position' => 2},
    'Field_3' => {'Datatype' => 'int', 'Position' => 3}
  },
  'Table_2' => {
    'Field_1' => {'Datatype' => 'float', 'Position' => 1}
  }
);

foreach my $table (sort keys %tables)
{
  foreach my $field (sort {$fields{$table}{'Position'}{$a} <=> $fields
+{$table}{'Position'}{$b}} keys %{$fields{$table}})
  {
    print "$table -> $field\n";
  }
}

[download]
This works in that the final "foreach" returns the fields in the order of the "Position" value but I don't understand why (I only got it to work by giving it a go!) or if it's safe to rely on. How does the hash of hashes find the "Position" value when the "fieldname" level has been skipped? That is: 
$fields{$tablename}{$fieldname}{'Position'}

[download]
and 
$fields{$tablename}{'Position'}

[download]
Can someone advise on why this works and whether it's safe to rely on? Thanks.

In reply to Sorting a hash by a well buried key by lb483

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.