Re: [PLUG] perl question

[Walt Mankowski <waltman@pobox.com>]

On Thu, Jan 20, 2011 at 02:44:37PM -0500, Eric at Lucii.org wrote:
> I have a data structure in perl:
> 
> @output
> 
> It is sparse (not all indexes have values.)
> 
> Those that do look like this example which would be something like $output[5]:
> $VAR1 = {
>           '128' => {
>                      'salutation' => 'Dr.',
>                      'area' => '800',
>                      'spec_link' => '131',
>                      'state' => 'PA',
>                      'last_name' => 'Smith',
>                      'dr_id' => '1',
>                      'city' => 'Swarthmore',
>                      'middle' => 'A',
>                      'active' => undef,
>                      'phone' => '555-1212',
>                      'description' => 'some description goes here',
>                      'sex' => 'M',
>                      'address2' => '',
>                      'loc_no' => '1',
>                      'zip' => '19067',
>                      'title' => 'DMD',
>                      'address1' => '123 Any Street.',
>                      'first_name' => 'John'
>                    }
>         };
> 
> When I put data in the element I do it like this:
> 
>    $var1 = 5 ; $var2 = 128 ;
>    $output[$var1]->{$var2}->{'description'} = "some description goes here" ;
> 
> To get the data out I walk through the array, skipping indexes where there is no
> data.  Once I find an array element with data I want to access the elements.
> Currently, the only way I can get to it is to use Dumper to produce the above
> print out.
> 
> How do I find out what the {'128'} value is so that I can address the elements?
> 
> I tried this:
> 
> for ( $x = 0; $x < $#output; $x++ ) {
>     next if not defined $output[$x] ;
>     $hashKey = keys $output[$x]  ;
>     print "record: $x has last name of: "
>        . $output[$x]->{$hashKey}->{'last_name'}  ;
> }
> 
> ... but perl barfs on the use of keys
> Type of arg 1 to keys must be hash (not array element) at ./build_fast_doc.pl
> line 229, near "]  ;"
> 
> What am I missing here?  I thought the array elements here ARE hashes.

No, the array elements are hash references, not hashes themselves.  So
you have to dereference it like so:

keys %{$output[$x]}

But your code would still have a problem, because keys returns a list,
not a scalar.  So if you wanted to save all the keys you'd need to do
something like

my @hashKeys = keys %{$output[$x]};

Oh, and your for loop has a bug as well.  If you have an array @a,
then $#a is the index of the last element in the array.  Since you
have < instead of <=, you're going to miss the final element.  You
hardly ever need to use C-style for loops in Perl, especially when
you're going through one element at a time.  I'd probably write the
loop as

for my $x (0..$#output)

Walt

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