Question

Thanks in advance for the help.

I have a array called %pepHash with 174 ‘counts’ and multiple ‘peptides’ in each $count.
Here’s a snippet of the hash:

Count: 39   Peptide: 0  Score: 55.03    MR: 1792.3206
Count: 39   Peptide: 1  Score: 75.22    MR: 1792.6158
Count: 39   Peptide: 2  Score: 62.63    MR: 1972.7156
Count: 39   Peptide: 3  Score: 49.95    MR: 2365.2174
Count: 40   Peptide: 0  Score: 46.38    MR: 1256.4437
Count: 40   Peptide: 1  Score: 71.07    MR: 1950.1644
Count: 40   Peptide: 2  Score: 71.77    MR: 2492.9394
Count: 40   Peptide: 3  Score: 67.28    MR: 2493.0154

Firstly, I’m not very good with data structures, so any better advice on multi-d hashes would be nice.

Count: 40   Peptide: 1  Score: 71.07    MR: 1950.1644 

is accessed by $pepHash[$count][$pepCount]{$PEP_SCORE} or {$PEP_MR}, and in this case it’s obviously $pepHash[40][1]{$PEP_SCORE}.
I want to sort all of %pepHash by its scores in descending order or create a new sorted hash so the list becomes:

Count: 39   Peptide: 0  Score: 75.22    MR: 1792.6158  
Count: 39   Peptide: 1  Score: 62.63    MR: 1972.7156 
Count: 39   Peptide: 2  Score: 55.03    MR: 1792.3206 
Count: 39   Peptide: 3  Score: 49.95    MR: 2365.2174
Count: 40   Peptide: 0  Score: 71.77    MR: 2492.9394 
Count: 40   Peptide: 1  Score: 71.07    MR: 1950.1644
Count: 40   Peptide: 2  Score: 67.28    MR: 2493.0154
Count: 40   Peptide: 3  Score: 46.38    MR: 1256.4437

Notice the updated $pepCount values. I have this loop which could be of use:

   for ($count = 0; $count < $total; $count++) {
      for ($pepCount = 0; $pepCount < $pepTotal[$count]; $pepCount++) {
      }
   }

I was also messing with this to no avail cause I’m a noob:

foreach $key (sort {$pepHash{$b} <=> $pepHash{$a}} keys(%pepHash)) {
   #CONFUSED
}

EDIT: This helped me a lot: http://www.stathis.co.uk/computers/perl-sort-tutorial

Answer 1

To store such data structures you may use hash of hashes. Here’s example:

my %pepHash;

$pepHash{someKey} = { Score => 100, Count => 42 };
$pepHash{someOtherKey} = { Score => 200, Count => 43 };
# ...

And then sort this hash:

foreach $key (sort {$pepHash{$b}->{Score} <=> $pepHash{$a}->{Score}} keys(%pepHash)) {
   my $data = $pepHash{$key};
   print "$key: Score - $data->{Score}, Count - $data->{Score}\n";
}

You may also want to read Perl documentation to feel yourself better with Perl data structures and perldoc -f sort to learn more about sorting in Perl.

Good luck!