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

Hi Monks, Can someone tell me what is Hash of Hash table? Can someone give me an example of that? I am trying to see if I can applay that when I try to have tow values as one key . I mean if I have a line in my file that look like this  one tow three four five six and I want to have one and tow as key for the rest of the line. right now I will have to have tow hashes as follow: 
%one;
%tow;
 while (<INPUT>) {
     chomp(my @line = split/\s+/);
         push @{$one{$r[0]}}, [ @line[1..$#r] ];
         push @{$tow{$r[1]}}, [ @line[2..$#r] ];
         }

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I need to some how merge it into one hash . Maybe if I understand Hash of Hash , I will be able to see if my approach is possible. Thanks all

Replies are listed 'Best First'.
Re: Hash of Hash
by jeffa (Bishop) on Feb 28, 2004 at 23:20 UTC
    A Hash of Hashes simply looks something like: 
    $ perl -MData::Dumper -e"%h=(a=>{1..4},b=>{5..8});print Dumper\%h"
$VAR1 = {
          'a' => {
                   '1' => 2,
                   '3' => 4
                 },
          'b' => {
                   '7' => 8,
                   '5' => 6
                 }
        };

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    What you probably want instead is a Hash of Lists. Try this: 
    use strict;
use warnings;
use Data::Dumper;

...

my %hash;
while (<INPUT>) {
   chomp;
   my @line = split /\s+/, $_;
   my ($key1,$key2) = (shift @line, shift @line);
   $hash{$key1} = $hash{$key2} = [@line];
}

print Dumper \%hash;

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    jeffa

    L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)
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Re: Hash of Hash
by neniro (Priest) on Feb 28, 2004 at 23:17 UTC
    I'm not sure, but you can use a reference for this purpose: 
    #!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

my $string = q(one tow three four five six);
my @words = split(/ /, $string);

my %hash1;
my %hash2;
$hash2{$words[1]} = join(" ", @words[2..5]);
$hash1{$words[0]} = \%hash2;
print Dumper(%hash1);

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    best regards neniro
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[d/l]
      Just a hint. Instead of
      my $string = q(one tow three four five six);
my @words = split(/ /, $string);

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      You might want to use
      my @words= qw(one tow three four five six);

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      As you no longer use $strings, there is no need for you to split on that.

      And as you don't really have a need for $hash2, this might help by using an anonymous hash:
      $hash1{$words[0]}= { $words[1] => join(' ', @word[2..$#words]) };

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Re: Hash of Hash
by Skeeve (Parson) on Feb 29, 2004 at 00:12 UTC
    To create a hash of hashes for that line, you can do this:
    my %hash_of_hashes= ( one => { two => 'three four five' } );

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    A hash of hashes is a simple hash, where each value is a pointer to another hash.
    To see how this looks like try this:
    use strict;
use warnings;
use Data::Dumper;

my %hash_of_hashes= ( one => { two => 'three four five' } );

print Dumper \%hash_of_hashes;

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