Hashes are great for statistics. In the following method, I use a string composed of the variety of keys to index the statistics: 
#!/usr/bin/perl -w
use strict;


my %hash = (
          'a' => {
                   'x' => 40,
                   'z' => 102
                 },
          'b' => {
                   'z' => 100,
                   'x' => 10,
                   'y' => 20
                 },
          'c' => {
                   'x' => 50
                 },
          'd' => {
                   'z' => 101,
                   'y' => 30
                 }
        );

sub stats {
    my %hhp = @_;
    
    my %counters; # a counter hash of which keys are used at level two
    
    foreach my $key1 (keys %hhp) {
        my @cList = ();
        foreach my $key2 (keys %{$hhp{$key1}}) {
            push(@cList,$key2);
        }
        ++$counters{join('+',sort @cList)};
    }
    return %counters;
}

#### main
my %result = stats(%hash);
foreach my $key (keys %result){
    print "$key $result{$key}\n";
}

[download]
The result looks like this: 
x+y+z 1
y+z 1
x+z 1
x 1

[download]
To do statistics on the actual values.. use the same logic.
perlcapt
-ben

In reply to Re: Counting hash of hashes elements by perlcapt
in thread Counting hash of hashes elements by albert

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