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

for my $family ( sort keys %HoH ) 
{
    print "$family: ";
   for my $role ( keys %{ $HoH{$family} } ) 
   {
         print "$role=$HoH{$family}{$role} ";
    }

   print "\n";

    print "$family: @{ $HoA{$family} }\n";
}

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The %HoA and the %HoH have the same keys, yet I get the error:
Can't use an undefined value as an ARRAY reference

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in the line: 
print "$family: @{ $HoA{$family} }\n";

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Replies are listed 'Best First'.
Re: What is wrong in this syntax?
by Athanasius (Archbishop) on Jun 30, 2014 at 02:14 UTC

    Works fine for me:

    #! perl
use strict;
use warnings;

my %HoH =
(
    Flintstone => { Father => 'Fred',  Mother => 'Wilma', },
    Simpson    => { Father => 'Homer', Mother => 'Marge', },
);

my %HoA =
(
    Flintstone => [ Father => 'Fred',  Mother => 'Wilma', ],
    Simpson    => [ Father => 'Homer', Mother => 'Marge', ],
);

for my $family (sort keys %HoH) 
{
    print "$family: ";

    for my $role (keys %{ $HoH{$family} })
    {
         print "$role=$HoH{$family}{$role} ";
    }

    print "\n";

    print "$family: @{ $HoA{$family} }\n";
}

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    Output:

    12:09 >perl 928_SoPW.pl
Flintstone: Father=Fred Mother=Wilma
Flintstone: Father Fred Mother Wilma
Simpson: Father=Homer Mother=Marge
Simpson: Father Homer Mother Marge

12:09 >

    [download]

    You will need to show the exact contents of %HoH and %HoA prior to the for loop. (Use Data::Dumper or Data::Dump.)

    Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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[d/l]
[select]
Re: What is wrong in this syntax?
by Laurent_R (Canon) on Jun 30, 2014 at 06:37 UTC
    It seems that it should work, unless your data structure is not exactly what you think. Please show a dump of your data structures (using Data::Dumper or an equivalent package or the x command of the Perl debugger).
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[d/l]
      Nah, sorry for that, it actually works fine, it was some stupid mistake of me :)
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Re: What is wrong in this syntax?
by Anonymous Monk on Jun 30, 2014 at 02:05 UTC
    I just tested it and the opposite thing actually works, i.e. 
    for my $family ( sort keys %HoA ) 
{
    print "$family: ";
    for my $role ( keys %{ $HoH{$family} } ) 
    {
         print "$role=$HoH{$family}{$role} ";
    }

    #print "\n";

    print "@{ $HoA{$family} }\n";
}

    [download]

    Now I am more confused...
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[d/l]

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