Re^3: Hash of Arrays or Arrays of arrays? and how proceed?

I'll try to give you a skeleton of that subroutine:

sub ExtractDatabaseFields {
  my $file= shift;
  my @databases= @_;
  my %result;
  foreach my $database (@databases) {
    my @fields= ... #extract data from database
    my $nextfield= .... #find next field
    $result{$database}{next}= $nextfield;
    $result{$database}{fields}= \@fields;
  }
  return \%result;
}

#-------------------
# Accessing

my $result= ExtractDatabaseFields($file,@databases);

#print next available field of database 27:
print $result->{"27"}{next}; 

#extract the fourth field from database 27:
my $field3= $result->{"27"}{fields}[3];

#add another field to database 27:                 
push @{$result->{"27"}{fields}}, "whatever"; 

#loop over the fields of database $x:
foreach $field ( @{$result->{$x}{fields}} ) { .... }
[download]

The resulting data structure would be a HashOfHashOfArrays, not a HashofArrays, but this makes the access to the data much clearer. If this isn't what you wanted you might give a more elaborate example

Comment on Re^3: Hash of Arrays or Arrays of arrays? and how proceed? Download Code

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Re^4: Hash of Arrays or Arrays of arrays? and how proceed? by paride (Initiate) on Aug 03, 2011 at 08:42 UTC
now all work ....but I realized I need a more complex solution... :( I've transformed $nextfield in an array because of two different DB could have 1 ore more fields less than the other one, and the result is OK! printing Dumper (when @Database is ("5","6"): $VAR1 = \'6'; $VAR2 = 'AP', 'AO' ; $VAR3 = 'AA', 'AB', 'AC', 'AD', 'AE', 'AF', 'AG', 'AH', 'AI', 'AJ', 'AK', 'AL', 'AM', 'AN' ; But to proceed correctly I need a different @fields($VAR3) for every database, and to reach the top of my desired target I would like to add other attributes to the sigle field. For example AA,5(dimension),N(numeric) etc. I know it's very complex jethro, when I start with the idea to do this script I didn't expect it will be so complex. But I think this could be an excellent way to learn perl in dept	[reply]
Re^5: Hash of Arrays or Arrays of arrays? and how proceed? by jethro (Monsignor) on Aug 03, 2011 at 10:12 UTC
Oh yes, you will be an expert on references and complex data structures after this ;-) One advice: You could store your attributes (i.e. AA, 5 'N' etc.) in strings (concatenated by ':' for example) or in arrays (i.e. index 0 would be 'AA', index 1 the dimension...). But usually the most maintainable way to do this is with a hash. `#add values $fields{$database}[$fieldno]{dimension}=5; $fields{$database}[$fieldno]{type}='N'; # check if an attribute 'something' exists if (exists $fields{$database}[$fieldno]{something}) {` [download]	[reply] [d/l]
Re^6: Hash of Arrays or Arrays of arrays? and how proceed? by paride (Initiate) on Aug 04, 2011 at 07:56 UTC
Thanks, I've choosen the string solution (AA,5,N...) and it work perfectly, but if I need to have a different @fields stored for each database? it works in sub but outside when I do the loop for each $Database to re-print dumper using `Dumper(\$Database,\@nextfield,\@fields);` It print only the fields of the "last" $Database acquired... did you have an idea about it?	[reply] [d/l]
Re^7: Hash of Arrays or Arrays of arrays? and how proceed? by jethro (Monsignor) on Aug 05, 2011 at 09:21 UTC
Re^8: Hash of Arrays or Arrays of arrays? and how proceed? by paride (Initiate) on Aug 05, 2011 at 11:39 UTC
Some notes below your chosen depth have not been shown here
Re^4: Hash of Arrays or Arrays of arrays? and how proceed? by paride (Initiate) on Jul 29, 2011 at 16:02 UTC
Excellent!!! Very Difficult... but Excellent!! THANK YOU VERY MUCH	[reply]
Re^5: Hash of Arrays or Arrays of arrays? and how proceed? by paride (Initiate) on Aug 01, 2011 at 16:02 UTC
...only another question (...for me it's not so clear...) using strict... if I declare in a sub my $variable and I need to return this $variable outside to use it with another sub, did I need to declare it outside the sub (i.e. our $variable)?	[reply]
Re^6: Hash of Arrays or Arrays of arrays? and how proceed? by moritz (Cardinal) on Aug 01, 2011 at 16:07 UTC
No, returning a value from a variable that goes out of scope is fine; the values are reference-counted and allocated on the heap. Perl 6 - second systems done right	[reply]
Re^4: Hash of Arrays or Arrays of arrays? and how proceed? by paride (Initiate) on Aug 02, 2011 at 09:58 UTC
I've got a compiling error on `$result{$database}{next}= $nextfield;` `$result{$database}{fields}= \@fields;` Use of uninitialized value in hash element but I've declared "my %result;" at the start of the sub Did I miss something? Did I need to declare $next and $fields?	[reply] [d/l] [select]
Re^5: Hash of Arrays or Arrays of arrays? and how proceed? by jethro (Monsignor) on Aug 02, 2011 at 11:13 UTC
The uninitialized value in hash element(!) would be $database. In such cases it is a good debugging technique to add statements like the following to your code to observe what happens: `use Data::Dumper; #at the start of the script ... print Dumper(\$database,\$nextfield,\@fields); $result{$database}{next}= $nextfield; $result{$database}{fields}= \@fi +elds; #<--- the problematic line` [download] A simple `print "\$database is $database\n"` would do as well, but Data::Dumper is to print for debugging like a lawnmower is to a scissor for cutting gras ;-). Look at the output and compare it to your expectations. Probably you will see an undef value printed for $database. Now you can retrace the steps, look how $database could get that value, insert "print Dumper..." statements where you think it could go wrong. Maybe it is a regex that didn't match anything or maybe you put a value in an array into `$a[1]` but not in `$a[0]`, which would leave the first array value undefined...	[reply] [d/l] [select]