Sad newbie question about Data::Dumper and array references..

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

Ok, before you click that -- button, cut me some slack here, I'm still new.

I'm misunderstanding Data::Dumper's output apparently, because I'm unable to look at an array reference properly. I've read the docs, but maybe I'm just too tired to see what's wrong. If someone could quickly point out my mistake, I'd be forever grateful.

I'm doing this:

    use Data::Dumper;  
    print Dumper($data);
[download]

And getting back this:

$VAR1 = [
          '0.001915',
          '0.000000',
          '0.007453',
          '0.000000'
        ];
[download]

So why does this

print $data[0];
[download]

return nothing? Shouldn't it return '0.001915'??

Thanks in advance. Sorry if this is Yet Another Ignorant Perl Question.

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Re: Sad newbie question about Data::Dumper and array references.. by busunsl (Vicar) on Mar 23, 2001 at 12:07 UTC
No, it shouldn't, because $data is holding a reference to an array. Try `print $data->[0];` [download]	[reply] [d/l]
Re: Re: Sad newbie question about Data::Dumper and array references.. by greenFox (Vicar) on Mar 23, 2001 at 13:10 UTC
other than style is there a reason to prefer `print $data->[0];` over `print @{$data}[0];` -- my $chainsaw = 'Perl';	[reply] [d/l] [select]
Re: Re: Re: Sad newbie question about Data::Dumper and array references.. by merlyn (Sage) on Mar 23, 2001 at 16:38 UTC
You want `${$data}[0]` [download] as the exact equivalent of `$data->[0]` [download] Otherwise you've just committed the famous `@foo[3]` sin, which much literature speaks of. -- Randal L. Schwartz, Perl hacker	[reply] [d/l] [select]
Re: Re: Re: Sad newbie question about Data::Dumper and array references.. by busunsl (Vicar) on Mar 23, 2001 at 13:54 UTC
Nope I just find `print $data->[0]` looks more like dereferencing.	[reply] [d/l]
Re: Re: Re: Sad newbie question about Data::Dumper and array references.. by geektron (Curate) on Mar 23, 2001 at 13:52 UTC
not that i can think of. there might be others to correct me, though. `print @{$data}[0]` is too many bracey-curly-making-me-hit-shift characters. they perform the same tasks.	[reply] [d/l]
Re: Re: Re: Re: Sad newbie question about Data::Dumper and array references.. by tomhukins (Curate) on Mar 23, 2001 at 15:28 UTC
Re: Re: Re: Re: Re: Sad newbie question about Data::Dumper and array references.. by greenFox (Vicar) on Mar 23, 2001 at 16:01 UTC
Some notes below your chosen depth have not been shown here
Re: Re: Re: Sad newbie question about Data::Dumper and array references.. by tadman (Prior) on Mar 24, 2001 at 00:42 UTC
It becomes apparent with more complex data structures, such as AoAoAoAoAoAoA's or HoHoHoHoHoHoHoH's, or any mutant variation thereof. `$data->[0]->[1]->[3]->[1]->[41]->[6]` over `${${${${${${$data}[0]}[1]}[3]}[1]}[41]}[6]` Unless you're really good at counting brackets, I'd stick with the C-style dereferencing via '->'	[reply] [d/l] [select]
Re: Sad newbie question about Data::Dumper and array references.. by Boldra (Deacon) on Mar 23, 2001 at 18:22 UTC
I'm surprised noone has told you to do this: #!/usr/bin/perl -w you would then have got this: `Use of uninitialized value in print at - line nn.` (because @data is undefined) Which should always make you suspicious.	[reply]
Re: Sad newbie question about Data::Dumper and array references.. by andye (Curate) on Mar 23, 2001 at 15:20 UTC
Clownburner, have a look at perlref, if you haven't already. The clearest explanation of reference syntax that I know of is in _Effective_Perl_Programming_ (Hall/Schwartz), that should make things much clearer. andy.	[reply]
Re: Sad newbie question about Data::Dumper and array references.. by I0 (Priest) on Mar 23, 2001 at 12:09 UTC
`print $data->[0];`	[reply] [d/l]
Re: Sad newbie question about Data::Dumper and array references.. by Anonymous Monk on Mar 25, 2001 at 00:12 UTC
The problem is that you are confusing a reference to an array with the array itself. Your $data variable is a scalar (not an array) whose value is a reference to an array. You need to use indirection to get at the elements of the array. These are all equivalent: `$$data[0] ${$data}[0] $data->[0]` [download] Personally, I prefer the third form but if you're trying to create obfuscated code use the first form.	[reply] [d/l]


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