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

Hi. How do I traverse a double hash? Namely, I put into a hash by 
myHash{Value1}{Value2} = foobar;

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I first traverse myHash on value1 by 
foreach my $key1 (sort keys %myhash)
{
  ## But now how do I traverse on key 2 based on key 1??
}

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Any help would be appreciated.

Replies are listed 'Best First'.
Re: Traversing a double hash
by btrott (Parson) on Apr 16, 2000 at 04:26 UTC
    Each value in the hash is a hash reference, so you need to dereference the hash reference, then just treat it like a regular hash. Take a look at perlref. Here's some code: 
    for my $key1 (sort keys %myhash) {
    print $key1, "\n";
    for my $key2 (sort keys %{$myhash{$key1}}) {
        print "\t", $key2, " => ", $myhash{$key1}{$key2}, "\n";
    }
}

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    If you just want to see what a data structure contains, use Data::Dumper: 
    use Data::Dumper;
print Dumper \%myhash;

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[d/l]
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      Just used this logic on a triple hash! Works beautifully! 
      for my $key1 (sort keys %linehash) {
    $outSect1 =  $key1;
    for my $key2 (sort keys %{$linehash{$key1}}) {
        $outSect2 = "$outSect1.$key2";
        print "$outSect2\n";
        for my $key3 (sort keys %{$linehash{$key1}{$key2}}) {
           if ($key3 ne ""){

              print "\t", $key3, " = ", $linehash{$key1}{$key2}{$key3}
+, "\n";
             }
           }
    }
}

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      Your humble servant,
      -Chuck
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[d/l]
      Thank you!
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Re: Traversing a double hash (kudra: some code)
by kudra (Vicar) on Apr 17, 2000 at 12:21 UTC
    I think you might be able to do this, if I correctly understood what you want to do: 
    # Assume you already have $key1
foreach $key2 (keys %{$myhash{$key1}}) {
   print "Key: $key2\nValue: ";
   print $myhash{$key1}{$key2}."\n\n"; 
}

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Re: Traversing a double hash
by zebroz (Initiate) on Apr 18, 2000 at 08:32 UTC
    Sweet thanks. :)
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