Array of Hashes or Hash of Arrays

perl@1983 has asked for the wisdom of the Perl Monks concerning the following question:

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Re: Array of Hashes or Hash of Arrays by jethro (Monsignor) on May 10, 2012 at 11:12 UTC
How would you get at a value from an Array of Hashes? You would first have to specify one of the hashes in the array and then the value in that particular hash. So, first an array access, then a hash access, right? A Hash of Arrays would be the other way round, first a hash access, then an array access. Now as in any computer language I know expressions are evaluated from inner to outer braces, for example 2+5 would be the first do be evaluated in (3+(7*(2+5)+4)). So look at your expression, what is the innermost expression, an array or hash access? What is the outer expression, array or hash access? Once you know that you know what structure it is.	[reply]
Re^2: Array of Hashes or Hash of Arrays by perl@1983 (Sexton) on May 10, 2012 at 11:32 UTC
Nice explanation Jethro. Thanks much.!!	[reply]
Re: Array of Hashes or Hash of Arrays by cdarke (Prior) on May 10, 2012 at 09:48 UTC
thing? `key_list_by_value` is a hash - you can tell by the { }. `$value` is a hash key (looks like someone did a `reverse()` on `%by_key`. `$key` is a scalar. `$key_list_by_value{$value}` is a reference to an array - hence the `@{ }`.	[reply] [d/l] [select]
Re^2: Array of Hashes or Hash of Arrays by perl@1983 (Sexton) on May 10, 2012 at 10:25 UTC
Didn't quite understand your last statement.. Can you please help to clarify? $key_list_by_value{$value} is a reference to an array - hence the @{ }.	[reply]
Re: Array of Hashes or Hash of Arrays by sumeetgrover (Monk) on May 10, 2012 at 11:15 UTC
Ok. Here's what seems to be happening in these two statements: 1. In the `while` loop, the pairs of Keys and Values from the hash `%by_key` are being fetched. 2. First things first: `$key_list_by_value{$value}`.`key_list_by_value` is a hash variable, which appears to contain array-refs, hence the use of `@{ }` around this variable. 3. What this second line of code is doing is that it is adding the current `$key` to the list pointed to by the current array-ref Here's the understandable version of this code: `while(($key,$value)=each(%by_key) { $current_key_list_aref = $key_list_by_value{$value}; push(@$current_key_list_aref,$key); }` [download]	[reply] [d/l] [select]