I think what I need is an Array of Array of Hash, but I have no idea how to make that.
Can Perl do that?
And if so, how would the code look like?
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2Why do you need to make an array of arrays of hashes? Sometimes if you tell us what you have to model we can help you figure out more specific examples (or if an AoAoH is right for that).brian d foy– brian d foy2010-09-09 19:58:46 +00:00Commented Sep 9, 2010 at 19:58
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4 Answers
perldoc perldsc is a good document to read to get an idea of data structures in Perl.
answered Sep 9, 2010 at 11:45
Alan Haggai Alavi
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Comments
You can address elements of such a data structure thus:
$x->[1][2]{foo} = "hello"
You don't even have to pre-define the structure. Just start working with the elements as if they're already there.
2 Comments
Alan Haggai Alavi
This feature of Perl is known as autovivification.
Ven'Tatsu
Please don't use the variable
$a (or $b) in examples that don't involve sort. $a and $b are special variables in Perl and can cause odd errors when used outside of a function passed to sort.my $aah =
[ # outer array
[ # first inner array
{ # first inner hash
foo => 'bar',
},
{ # second inner hash
bar => 'baaz',
},
],
[ # secnd inner array
#...
],
# ...
];
You can access the elements like this:
$aah->[0]->[1]->{bar} # => 'baaz'
3 Comments
Axeman
Or
$aah->[0][1]{bar}... everything in an array or hash is a scalar, thus any substructures can be assumed to be references, thus only the first arrow is ever needed.
Dummy00001
Or
$$arr[0][1]{bar}. I personally prefer that over the -> notation.
MkV
This doesn't need to be an array reference, replace the first [ with ( the last ] with ) and $aah with @aah. Now you can access the data like this: $aah[0][1]{bar}; no de-referencing syntax needed, for the reason stated by Axeman.
my $arr =
[
[
{key1 => $value1, key2 => $value2},
{key1 => $value3}
],
[
{rubbish => 'nonsense'},
]
];
etc.
3 Comments
MkV
Just because its a nested data structure doesn't mean it needs to be an arrayref, it can be an array of arrayrefs of hashrefs.
Marcelo Cantos
@MkV: Most programmers would prefer the arrayref, since it's cheaper and simpler to pass around as a data structure than a list would be. BTW, did you downvote this answer? If so, that's a pretty lame reason to do so.
Colin Fine
Of course it can be an array rather than an arrayref at the top. So what? It doesn't change the answer in any significant way. I don't know why you felt it necessary to add that comment to my and jkramer's answers.
