returning nested data structures

brp4h has asked for the wisdom of the Perl Monks concerning the following question:

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Re: returning nested data structures by suaveant (Parson) on Dec 22, 2009 at 21:13 UTC
Well, not all of your code is here, so its hard to tell, but if you mean to return the hash as a reference you need a return \%filters;, if not you need to do %hash = Module::method(); since you will be returning as a list. But more importantly, are you sure there is any data in the hash at the end? Use some print statements or even better change return %filters to: `use Data::Dumper; print STDERR Dumper(\%filters); return %filters;` [download] To make sure you actually have data! - Ant - Some of my best work - (1 2 3)	[reply] [d/l]
Re: returning nested data structures by toolic (Bishop) on Dec 22, 2009 at 21:15 UTC
When you say 'module', do you really mean 'sub'? If so, you should show how you are calling your sub. This is a way to return a hash-of-arrays from a sub: `use strict; use warnings; my %filt = foo(); use Data::Dumper; print Dumper(\%filt); sub foo { # Create a hash-of-arrays my %filters = ( a => [0..2], b => [3..5] ); return %filters; } __END__ $VAR1 = { 'a' => [ 0, 1, 2 ], 'b' => [ 3, 4, 5 ] };` [download] You could also return it as a reference to a HoA.	[reply] [d/l]
Re: returning nested data structures by jethro (Monsignor) on Dec 22, 2009 at 21:17 UTC
What you may not know about the return function is that it evaluates its parameter(s) in the context of the subroutine invocation. If you called the subroutine like this: `$f= sub(...)` then %filters will be evaluated in a scalar context and return a string that shows some statistics of the hash, but no values of the hash itself. To rectify this you can do one of two things: Return a reference to the hash instead of the hash, i.e. "`return \%filters;`". Or change the call context, i.e. "`%f= sub(...)`". The second method copies the complete hash and should be avoided if the hash is really big	[reply] [d/l] [select]
Re: returning nested data structures by fzellinger (Acolyte) on Dec 22, 2009 at 21:17 UTC
Try returning a reference to the hash: `return \%filters;` Other things to do: Begin your code with: `use strict;` Initialize filters: `my %filters=();` Add some print statements. Dump %filters prior to returning it just to check: `use Data Dumper; print Dumper(\%filters);` [download]	[reply] [d/l] [select]
Re: returning nested data structures by brp4h (Acolyte) on Dec 22, 2009 at 21:45 UTC
Sorry - I tried returning `\%filters` first, but that didn't work. The code I posted is in a sub within a module, because I need to use it in several programs. Here's what I'm doing in the main program (when returning \%filters): `my($filters_ref) = GetFilters($filters_file); %filters = %$filters_ref; print \%filters; foreach (keys %filters) { print; }` [download] I get a hash reference with the first print line but nothing with the second. I've tested the data in the hash and it's perfectly correct before I return it.	[reply] [d/l] [select]
Re^2: returning nested data structures by gube (Parson) on Dec 22, 2009 at 22:32 UTC
Hi, 1) Can you print Dumper(\%filters) and check whether its reference of reference. 2) Otherwise, try foreach (keys %{$filters_ref}) { print; } and see it works Gubs	[reply]


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