Re^2: How to (get started on) sort AoA or AoH by frequency

Whew... This is intense.

I'm sorry, but I've tried, and read some articles on hashes/data structures, but still need some assistance understanding this.

I get the map statement. But:

$unique_descriptive{$num}{count}++;
   push @{$unique_descriptive{$num}{values}}, $num;
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Is a little confusing.

Here's what I got so far: The first statement increments the value of "count"(which I guess is a new key made then and there?). The value is in the HoH %unique_descriptive, at the key: That is the number, which is the element of the de-referenced array being looped through.

Then the 2nd line is AoHoH?? But that array is never used later? The keys of the most inner hash are the values of something(what?). The end value of this is the number from the loop being pushed in. The 2nd inner hash is at the key of $num. Was the @ in front only necessary b/c push takes list context?

Then the other problem is:

my @sorted_keys = sort{ $unique_descriptive{$a}{count} <=> $unique_des
+criptive{$b}{count} 
                                                        or
                                                     $a <=> $b
                      }keys %unique_descriptive;
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The numbers are being sorted based on count first (did you know to put $a where it is b/c $num was there before?) And if that is equal, the numbers themselves are compared. The keys are being sorted.

Sorry for the trouble I'm having with this, I hope I was close/this makes sense to you.

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Re^3: How to (get started on) sort AoA or AoH by frequency by Marshall (Canon) on Jun 13, 2011 at 20:53 UTC
The first statement increments the value of "count"(which I guess is a new key made then and there?). Yes. Perl will "autovivify" a new entry if none already exists. The is pretty cool stuff. In other languages I would have had to size and initialize the structure. In Perl, I can just do that as I go. But that array is never used later? Correct. My code produces exactly the same structure as your code, but in more understandable way (at least for me!). The "values" really aren't needed (and yes this is an @array). I just did that because your code did it. The "values" will always be the same as the number key and always repeated the same times as the frequency. That could easily be computed. So really all that is needed is a single dimensional hash instead of two dimensions (see my code later in the thread). update: I'm not sure about your understanding of sort... Trying to further clarify... $a and $b are two hash keys that sort chooses for us - these are some chosen set of number pairs. We don't have to be concerned with the algorithm that sort uses, we just have to tell it how to compare a and b.	[reply]

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Re^3: How to (get started on) sort AoA or AoH by frequency
by Marshall (Canon) on Jun 13, 2011 at 20:53 UTC

The first statement increments the value of "count"(which I guess is a new key made then and there?).

Yes. Perl will "autovivify" a new entry if none already exists. The is pretty cool stuff. In other languages I would have had to size and initialize the structure. In Perl, I can just do that as I go.

But that array is never used later?

Correct. My code produces exactly the same structure as your code, but in more understandable way (at least for me!). The "values" really aren't needed (and yes this is an @array). I just did that because your code did it. The "values" will always be the same as the number key and always repeated the same times as the frequency. That could easily be computed. So really all that is needed is a single dimensional hash instead of two dimensions (see my code later in the thread).

update:
I'm not sure about your understanding of sort... Trying to further clarify... $a and $b are two hash keys that sort chooses for us - these are some chosen set of number pairs. We don't have to be concerned with the algorithm that sort uses, we just have to tell it how to compare a and b.

[reply]