Populating Arrays of Arrays

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

Greetings Monks

This is a foray into 3 dimensional data structures. The aoa in question is at the end, I can't seem to sort out my references and dereferences.Guidence is order,I'm not sure where this leads or how I am thinking incorrectly.
I also have a bit of confusion surounding strictures: Why does a scalar defreference of an array force declarations to be made on the scalar and the array with the scalar name?Seems redundant,but strict seems important in the future of my studies.
Thanks

#! /usr/bin/perl

use strict;
use warnings;

#a plethora of my's ...strict baffles me

my @contents;
my @aoa;
my @ctags;
my @ctagarray;
my @aoac;
my @headc;
my @contentc;
my @fontc;
my @scalarclose;
my $ctag;
my $font;
my $head;
my $content;
my $val;
my $newlength;
my $count;
my $scalarclose;
my $headc;
my $fontc;
my $contentc;
my $i;

#two arrays of arrays to populate

@aoa=qw/header font content/ ;
@aoac=qw/headerc fontc contentc/;

# array of array values

@contents=( ["html","head","body",],
            ["font","face","size","color"],
            ["h1","p","code"]
            );

#scalar ref to array for later population

 $scalarclose=\@aoac;

#populate  the aoa

        for (0...$#aoa){
        $aoa[$_]=$contents[$_];
        }

#use contents of populated aoa

 foreach $val(@aoa){

# an incrementer hacked to use for populating
# an aoa with modified values

 ++$i;
 $count=$i-1;

#get values from original aoa and modifiy,
#begin population of new aoa

 our $length=scalar @$val;
 for (0...$length-1){
        $ctag="<\\$val->[$_]>";
        push @ctags ,$ctag ;
        }


    $newlength=$length+1;
    @ctagarray=splice @ctags,0,$newlength;

#this line is problematic

   @$scalarclose[$count]=map {$_}, @ctagarray;

  }

#scalar refs to aoa

$headc=$aoac[0];
$fontc=$aoac[1] ;
$contentc=$aoac[2];

#print to see the populus >>broken<<

print  " $headc->[1]\n";
print  " $fontc->[1]\n";
print  " $contentc->[1]\n";
[download]

Comment on Populating Arrays of Arrays Download Code

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Re: Populating Arrays of Arrays by Tanktalus (Canon) on Mar 03, 2005 at 19:11 UTC
You have: `#this line is problematic @$scalarclose[$count]=map {$_}, @ctagarray;` [download] I'm zeroing in on this. What you probably want is: `@$scalarclose[$count]=[map {$_}, @ctagarray];` [download] An array can only hold a scalar, even if that scalar is actually a ref to something else. In this case, I've made the scalar into a ref to an anonymous array. Note that you have way too many declarations up front. Try moving the "my" closer to where each variable is first used. This is Perl, not Pascal. Thanks.	[reply] [d/l] [select]
Re^2: Populating Arrays of Arrays by husker (Chaplain) on Mar 03, 2005 at 19:59 UTC
Note that you have way too many declarations up front. Try moving the "my" closer to where each variable is first used. This is Perl, not Pascal. Thanks. Is that really a big deal? I declare the same way (although I will group declarations together).	[reply]
Re^3: Populating Arrays of Arrays by Mugatu (Monk) on Mar 03, 2005 at 20:56 UTC
Is that really a big deal? It's indicative of a weak understanding of lexical scope. It's a symptom of a problem, not a problem in and of itself. Putting a huge block of my declarations at the top of the file is not a whole lot better than using package variables for everything. About the only benefit you get from strict is checking for typos. I prefer to scope variables as tightly as possible. That means, at the latest possible time and smallest possible block for the code to still work. Then, not only do I get protection against typos in variable names, I also get protection against inadvertant action-at-a-distance.	[reply]
Re: Populating Arrays of Arrays by davis (Vicar) on Mar 03, 2005 at 19:48 UTC
Yikes. I don't intend to be rude at all, but your code is difficult to read and understand. I tried re-writing it, and I got this far: `#!/usr/bin/perl use warnings; use strict; use diagnostics; use Data::Dumper; my @contents = ( [qw/html head body/], [qw/font face size color/], [qw/h1 p code/]); my @ctags; foreach my $row (@contents) { #$row will now be an array reference; #print Dumper $row; # if you want to see foreach my $value (@$row) { push @ctags, "<\\$value>"; } } print Dumper(\@ctags);` [download] To be honest, I'm not sure of your actual intentions in the scalarclose line, and the rest of the code features a lot of redundancy. What are your ultimate intentions? How close is this to doing what you want? Hint: Using Data::Dumper is a great way to see your variables' values. davis It wasn't easy to juggle a pregnant wife and a troubled child, but somehow I managed to fit in eight hours of TV a day.	[reply] [d/l]
Re^2: Populating Arrays of Arrays by dReKurCe (Scribe) on Mar 03, 2005 at 19:55 UTC
The object was to gain understanding of AOAs and strict. No long term plan for this particular piece of code. Thanks for taking the time to hack through my obtuse dialect.I'll pick up on your code and extract ideas for efficiency.	[reply]
Re^3: Populating Arrays of Arrays by davis (Vicar) on Mar 03, 2005 at 20:03 UTC
Ah ok. Couldn't really see the eventual purpose :) General notes: declare "my" variables as late as possible: if you declare them inside a block (~~delineated~~ delimited by braces), the variable won't be accessible (generally speaking) outside that block: `my $foo; if($somevalue) { my $bar = "baz"; $foo = "monkey"; }` [download] In this piece of code, $bar is only accessible inside the `if` block. $bar, on the other hand, will disappear (or "go out of scope") as soon as the compiler reaches the closing "}". Declaring variables as late as possible is generally considered a Good Thing (this is probably an oversimplification, but it's a good start). I know I've said it already, but `use Data::Dumper;` to inspect variables. If you show what eventual output you want from this code, you'll probably get a response showing you one way of getting it. davis It wasn't easy to juggle a pregnant wife and a troubled child, but somehow I managed to fit in eight hours of TV a day.	[reply] [d/l]
Re: Populating Arrays of Arrays by dmorelli (Scribe) on Mar 03, 2005 at 19:38 UTC
#a plethora of my's ...strict baffles me You can group them together like this: `#a plethora of my's ...no longer so baffling my (@contents, @aoa, @ctags, @ctagarray, @aoac, @headc, @contentc, @fo +ntc, @scalarclose); my ($ctag, $font, $head, $content, $val, $newlength, $count, $scalarcl +ose, $headc, $fontc, $contentc, $i);` [download]	[reply] [d/l]
Re: Populating Arrays of Arrays by osunderdog (Deacon) on Mar 03, 2005 at 20:28 UTC
First off, it is very good that you started with `use strict`! It'll definitely help you straighten these things out sooner than later. In answer to your question Why does a scalar defreference of an array force declarations to be made on the scalar and the array with the scalar name? Yes if you dereference an array and want to keep track of that reference, it'll have to be assigned into a scalar. However that scalar name doesn't have to correspond to the array name in any way. Perhaps a written description of what you're trying to accomplish would help us figure out how to extrapolate what you have into what you want. I can give you some ideas that may help... In my experience seeing that many variable declarations is a flag that the code can be simplified. Generally when I see looping structures like: `for (0...$#aoa)` or `our $length=scalar @$val; for (0...$length-1)` [download] that it may be possible to loop over an array (ie `for my $item (@aoa)` rather than the indicies of that array. You can populate a complex structure without having to assemble it as you are doing. For example where you are populating `@aoa` and then populating `@contents` and then looping through `@aoa` assigning elements to items out of `@contents` could be written: `my @aoa = ('header',['html','head','body',], 'font',['font','face','size','color'], 'content',['h1','p','code'])` [download] But this makes me think that you really wanted a Hash of Arrays (HoA) rather than an Array of Arrays (AoA). Which would be: `my %hoa = ('header',['html','head','body',], 'font',['font','face','size','color'], 'content',['h1','p','code'])` [download] There are other things...but that's all I've got time for for now... *"Look, Shiny Things!"* is not a better business strategy than compatibility and reuse.	[reply] [d/l] [select]
Re: Populating Arrays of Arrays by jdporter (Paladin) on Mar 03, 2005 at 22:27 UTC
In addition to all the other fine advice given in this thread... `#two arrays of arrays to populate @aoa=qw/header font content/ ; @aoac=qw/headerc fontc contentc/;` [download] Those are not arrays of arrays. They're simply arrays (that is, arrays of scalars). If you haven't done so lately, I highly recommend you read perlreftut, perllol, perldsc, and perlref (in that order).	[reply] [d/l]
Re: Populating Arrays of Arrays by Roy Johnson (Monsignor) on Mar 03, 2005 at 22:07 UTC
I have modified your code and added comments (with ) to let you know what's changed and what you might have misunderstood. Hope this helps. Read more... (3 kB) Caution:** Contents may have been coded under pressure.	[reply] [d/l]


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