In fact, you might want to use more descriptive names in your while statement:

my %freq;

while (my ($page, $hits) = $cursor->fetchrow_array) {
  $freq{$page} = $hits;
}
[download]

Perl calls "associative arrays" hashes. It makes sense and it saves you a bunch of syllables to use at a later date.

Yes to the latter, maybe to the former. The fact that associative arrays in perl are implemented using a hashing mechanism, is just an implementation detail that has no influence on how people use them. So I'm more or less unhappy with that name.

I'd prefer "string-indexed arrays" any day, but of course, people with find that name too long, too.

I wouldn't mind "map" (except that's overloaded) or "mapping", and Python calls them (or at least used to call them) "dictionaries", which also makes sense (except you tend to think of a dictionary as being sorted alphabetically).

---

Jeff japhy Pinyan, P.L., P.M., P.O.D, X.S.: Perl, regex, and perl hacker
How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart

This is one way:

while (@_ = $cursor->fetchrow) {
  $freq{$_[0]}=$_[1];
}
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What happens is you are associating the result to an anonymous array (@_)

my %page_hits;
while (my ($page_title, $hit_count) = $cursor->fetchrow_array) {
    $page_hits{$page_title} = $hit_count;  
}
[download]

Cheers,
Darren :)

Thanks Jeff & Darren,
I understand this part, that sets the 2 variables to the 2 fields:

while (my ($page_title, $hit_count) = $cursor->fetchrow_array) {
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I assume the next line is setting the page_hits hash, with the index being $page_title and the value being $hit_count, right?

Next dumb question, what is the '%' in front of the page_hits?, and why use 'my'?
Sorry for the ignorance , this is certainly not PHP :)

The % tells perl that it is a hash (not a regular array, @, or a scalar, $). In perl, %var is different than $var is different than @var. So you can have all three if you want.

"my" declares a lexical scope. You should really read up on "use strict" "use warnings" and scoping. There are tons of articles on the web and on this site.

In regards to this specific use of "my" - it makes the two variables visible to only the inside of said while loop. If you have on "strict" and "warnings" and you try to print $page_title AFTER the end of the while loop, you will get an error, because the variable has gone out of scope.

It's not like PHP where you can make a variable inside a huge nested loop/function and have it visible outside of said loop or function.

my %page_hits;
while (my $row = $cursor->fetchrow_hashref) {
    $page_hits{$row->{page_title}} = $row->{hit_count};  
}
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# Assuming you like the idea of scoping two variables
# lexically within the while block as noted in previous
# comments
while ( my ( $page_title, $hit_count ) = @{ $cursor->fetchrow_arrayref
+() } ) {
    $page_hits{$page_title} = $hit_count;
}
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Wouldn't using fetchrow_arrayref, then immediately enclosing it in an @{} defeat the purpose of getting and array ref in the first place?

while ( my $ref = $cursor->fetchrow_arrayref ) {
    $page_hits{$ref->[0]} = $ref->[1];
}
[download]

In the special case where I have a select statement that will return key/value pairs, I usually use this syntax:

  use strict;
  use warnings;
# I assume you have already established your database handle
  my $statement = "select my_key, my_value from my_table";
  my $ary_ref = $db_handle->selectcol_arrayref($statement, { Columns=>
+[1,2] });

  if ($DBI::errstr) {
    #do something
  }
  my %lookup_table = @$ary_ref if ref($ary_ref) eq 'ARRAY';
[download]

This has the happy result of creating a reference to an array which can be treated as a series of key/value pairs, and thus can directly populate my hash table. I think it is a nice, readable shortcut.

mindblowing stuff :)

can someone pass the aspirin

would anyone be able to anwser my 2 daft questions from earlier too please?, the ones about my and %

@ is a sigil, indicating an array. $ is a sigil indicating a scalar. % is a sigil indicating a hash (an associative array).

• $variable is a scalar.
• @variable is an array.
• %variable is a hash.

my creates a lexically scoped variable.

Important: You won't be able to just guess at this stuff. perlintro is required reading, if you plan to actually hammer out a few lines of Perl code.




Dave

Thanks, don't get me wrong -I am heavily reading up on all of this, its just that I'm jumping straight into a minor project in order to force myself to learn.
I'm reading O'Riellys Llama book, and I'm only on chapter 4. I notice if I had reached chapter 6 I would have answered my hashes questions.

Thanks for answering my extremely fundamental questions.

I appreciate that there are security considerations also, but at present I'm just ploughing through code, making things clearer as I go.