o2bwise has asked for the wisdom of the Perl Monks concerning the following question:

Hi,

I made a perl mod called regression that takes a pointer to a hash of x,y data pairs when it is blessed. I tested it with a simple program and verified that it runs with that program. Here is part of the simple program code…

my %raw_data = (
    1    =>    100,
    2    =>    160,
    2.5    =>    182,
    3    =>    225
    );


my $regr = regression->new(\%raw_data);
print '$regr= ', Dumper($regr);

$mean_x = $regr->get_mean_x;
print '$mean_x= ', Dumper($mean_x);

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and here is some of the output. (The numbers are all correct.) 

$regr= $VAR1 = bless( {
                 'mean_y' => '166.75',
                 'raw_data' => {
                                 '1' => 100,
                                 '3' => 225,
                                 '2' => 160,
                                 '2.5' => 182
                               },
                 'slope' => '60.6285714285714',
                 'mean_x' => '2.125',
                 'y_intercept' => '37.9142857142857'
               }, 'regression' );

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Well, I try it with a work example, which requires a more complicated hash structure.

Here is where the hash is populated: 

        $raw_dataPtr = \%{$element_stats_hash{$element_name}{'raw_data
+'}};
        $$raw_dataPtr{$time} = {$var};

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So, the hash key is set to the values in variable $time and the hash value is set to values in variable $var.

Here is where the object is blessed into existence: 

    #$regr = regression->new(\%{$element_stats_hash{$element_name}{'ra
+w_data'}});
    $regr = regression->new(\%{$element_stats_hash{$element_name}});
    print TEST '$regr= ', Dumper($regr);

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I have also tried this: 

    $regr = regression->new(\%{$element_stats_hash{$element_name}});
    print TEST '$regr= ', Dumper($regr);

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Here is the output of the class’s hash data structure (either way): 

'raw_data' => {
                                                 '1229265435' => {
                                                                   '0.
+12205589' => undef
                                                                 },
                                                 '1229299036' => {
                                                                   '0.
+71940041' => undef
                                                                 },
                                                 '1229317107' => {
                                                                   '1.
+22392523' => undef
                                                                 },

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Of course, I WANT it to look like this: 

'raw_data' => {
                                                 '1229265435' => '0.12
+205589',
                                                 '1229299036' => '0.71
+940041',
                                            '1229317107' => '1.2239252
+3'
                                                                 },

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and I just cannot seem to understand what is going on here. Might someone be able to explain to me what I need to do in order to get the hash in the class to look like I want it to? And can someone explain what is presently going on?

Many thanks in advance.

Tony

Replies are listed 'Best First'.
Re: Confounded With A Simple Self-Made Perl Mod
by GrandFather (Saint) on Dec 15, 2008 at 23:18 UTC

    I suspect you want:

    $regr = regression->new($element_stats_hash{$element_name});

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    which I'm guessing is already a reference to a hash of your raw data.

    It looks like you are going out of your way to make things complicated by wrapping \%{} around things that are already hash references. For example:

    $raw_dataPtr = \%{$element_stats_hash{$element_name}{'raw_data'}};
$$raw_dataPtr{$time} = {$var};

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    would be much better as:

    $element_stats_hash{$element_name}{'raw_data'}{$time} = {$var};

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    except that {$var} is wrong in any case. You really must use strictures (use strict; use warnings;)! With strictures that line would generate something like:

    Odd number of elements in anonymous hash at noname.pl line 8.

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    Perl's payment curve coincides with its learning curve.
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[d/l]
[select]
Re: Confounded With A Simple Self-Made Perl Mod
by almut (Canon) on Dec 15, 2008 at 23:17 UTC 
    $raw_dataPtr = \%{$element_stats_hash{$element_name}{'raw_data'}};
$$raw_dataPtr{$time} = {$var};

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    I think you want something like this: 

    #!/usr/bin/perl

use Data::Dumper;

my $time = time();
my $val  = 0.12205589;
my $element_name = "foo";

$element_stats_hash{$element_name}{'raw_data'}{$time} = $val;   # <--

print Dumper $element_stats_hash{$element_name};

__END__
$VAR1 = {
          'raw_data' => {
                          '1229382894' => '0.12205589'
                        }
        };

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    Update: That said, there's nothing wrong with using an intermediate variable, in particular if you should end up needing it multiple times: 

    # init raw data hash somewhere
$element_stats_hash{$element_name}{'raw_data'} = {};

# then later
my $raw_data = $element_stats_hash{$element_name}{'raw_data'};
$raw_data->{$time} = $val;
$raw_data->{$another_time} = $another_val;
#...

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    But note the difference with respect to autovivication... which is why we need to init an (empty) 'raw data' hash in this case, before we can take a ref to it.

    Also, please use the arrow syntax for dereferencing — it's much more readable (and less ambiguous) than $$raw_data{$time} when the expressions get more complex...

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[d/l]
[select]
      Hi,

      Thanks. I believe I tried your suggestion carefully and it still does the same thing.

      ???

      Tony
[reply]

        Could you post the exact code you tried?  Anything else would require mind reading on our part to figure out where the problem lies :)  — Self-contained snippets are always preferred...

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