Re: Creating a hash of arrays from row data

[Sudarshan Raghavan]

Rob Anderson wrote:

Hi Jeroen,

 

while (@values = $lcsr->fetchrow) {
   

This is probably the root of your problem every time you go through this
loop, you are repopulating your array, put a my before @values.
Why do you think this is a problem? All the my would do is create a new 
lexical @values in every iteration.
What do you mean by repopulating @values? my @values = ... would also 
populate @values.
Am I missing something?

 

  $key = shift @values;
  $key.= shift @values;
  push @$ref_to_a, [EMAIL PROTECTED];
   

I don't recognise this format, I'd have done this line as.
push @$ref_to_a, [EMAIL PROTECTED];
[EMAIL PROTECTED] creates an anonymous arrayref by copying the values stored in 
@values. perldoc perlref, perldoc perllol

If you are going use this statement
push @{$ref_to_a}, [EMAIL PROTECTED];
your while condition must be while (my @values = ...)
If you are going to use
push @{$ref_to_a}, [EMAIL PROTECTED];
you can leave the while condition as while (@values = ...)
Reason: 'shallow copying' vs 'deep copying'
Read through this link
http://www.stonehenge.com/merlyn/UnixReview/col30.html


 

  if ($old_key ne $key) {
      $hash{$key} = $ref_to_a;
      my $ref_to_a = undef;
  }
  $old_key = $key;
}
   



Having made these comments, I haven't really understood your logic or the
need for your, old_key values. I'd have done something like the following.
while (my @row_data = $lcsr->fetchrow ) {

while (my ($key1, $key2, @row_data) = $lcsr->fetchrow) {

   $key = shift @row_data;
   $key.= shift @row_data;
   # create top level array if this is the first time we've seen this key
   if (! defined $data{$key}) {$data{$key} = []}
This is not neccessary, when you assign to a non-existent hash key, perl 
will create the key for you

   my $array_ref = $data{$key};
   push(@$array_ref, [EMAIL PROTECTED]);
 

You can replace the code inside the while block with
push (@{$data{$key1 . $key2}}, [EMAIL PROTECTED]);
Your final code will be
while (my ($key1, $key2, @row_data) = $lcsr->fetchrow) {
   push (@{$data{$key1 . $key2}}, [EMAIL PROTECTED]);
}
}

Hope this helps

Rob Anderson



 



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