Re: inverting keys in a 2-D Hash

I can't imagine doing this myself after so carefully constructing a hash to index my data, but, this will do what you want:

foreach my $key ( keys %hash ) { 
  while ( my ( $subkey, $value ) = each %{ $hash{$key} } ) { 
    $hash{ $subkey }{ $key } = $value;
  }
  delete $hash{ $key };
}
[download]

But what about when there are multiple occurrences of keyB in the original hash? Or multiple subkeys in the subhashes?

#!/usr/bin/perl
use strict;
use warnings;
use feature qw/ say /;
use Data::Dumper;

my %hash;
$hash{'keyA'}{'keyB'} = '1234';
$hash{'keyC'}{'keyB'} = '5678';

say Dumper \%hash;

foreach my $key ( keys %hash ) { 
  while ( my ( $subkey, $value ) = each %{ $hash{$key} } ) { 
    $hash{ $subkey }{ $key } = $value;
  }
  delete $hash{ $key };
}

say Dumper \%hash;

__END__
[download]

Output:

$VAR1 = {
          'keyA' => {
                      'keyB' => '1234'
                    },
          'keyC' => {
                      'keyB' => '5678'
                    }
        };

$VAR1 = {
          'keyB' => {
                      'keyC' => '5678',
                      'keyA' => '1234'
                    }
        };
[download]

.... is that really what you want?

The way forward always starts with a minimal test.

Comment on Re: inverting keys in a 2-D Hash Select or Download Code

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Re^2: inverting keys in a 2-D Hash by melmoth (Acolyte) on Aug 30, 2015 at 22:01 UTC
Yes this is exactly what I want. I have rna sequences that have been aligned to dna so each rna has associated with it a number of dna but other rna sequences may also align to some of these dna sequences. The original keys tell me what dna is aligned to each rna but i want to see, for each dna, what rna it has been aligned to.	[reply]
Re^3: inverting keys in a 2-D Hash by 1nickt (Canon) on Aug 31, 2015 at 05:29 UTC
#!/usr/bin/perl use strict; use warnings; use feature qw/ say /; my %hash; $hash{'rna1'}{'dna1'} = '1111'; $hash{'rna1'}{'dna2'} = '1111'; $hash{'rna2'}{'dna1'} = '2222'; $hash{'rna3'}{'dna1'} = '2222'; $hash{'rna3'}{'dna2'} = '4444'; $hash{'rna2'}{'dna3'} = '3333'; say 'Report by RNA:'; foreach my $rna ( sort keys %hash ) { say " $rna has:"; foreach my $dna ( sort keys %{$hash{$rna}} ) { say " $dna = $hash{$rna}{$dna}"; } } say ''; # reverse the hash my %hash2 = %hash; foreach my $key ( keys %hash2 ) { while ( my ( $subkey, $value ) = each %{ $hash2{$key} } ) { $hash2{ $subkey }{ $key } = $value; } delete $hash2{ $key }; } say 'Report by DNA:'; foreach my $dna ( sort keys %hash2 ) { say " $dna is in:"; foreach my $rna ( sort keys %{$hash2{$dna}} ) { say " $rna with $hash2{$dna}{$rna}"; } } say ''; __END__ [download] $ perl 1140433.pl Report by RNA: rna1 has: dna1 = 1111 dna2 = 1111 rna2 has: dna1 = 2222 dna3 = 3333 rna3 has: dna1 = 2222 dna2 = 4444 Report by DNA: dna1 is in: rna1 with 1111 rna2 with 2222 rna3 with 2222 dna2 is in: rna1 with 1111 rna3 with 4444 dna3 is in: rna2 with 3333 $ [download] The way forward always starts with a minimal test.	[reply] [d/l] [select]
Re^2: inverting keys in a 2-D Hash by melmoth (Acolyte) on Aug 30, 2015 at 21:49 UTC
Thanks everyone some good ideas	[reply]