Sorting Hash of Hashes by value - arrays

Question

I have the following data structure
my %HoH = {
'foo1' => {
'bam' => 1,
'zip' => 0,
},
'foo2' => {
'bam' => 0,
'zip' => 1,
'boo' => 1
}
};
I would like to sort KEY1 (foo1 or foo2) by the VALUE stored in 'zip' in order from greatest to least.
Here's how I'm doing it.
use strict; use warnings;
use Data::Dumper;
my #sorted;
foreach my $KEY1 (keys %HoH) {
# sort KEY1 by the value 'zip' maps to in descending order
#sorted = sort {$HoH{$KEY1}{'zip'}{$b} <=>
$HoH{$KEY1}{'zip'}{$a}} keys %HoH;
}
print Dumper(\#sorted);
I'm getting an weird warning: Reference found where even-sized list expected at test.pl line 6.
Also print Dumper(\#sorted); is printing
$VAR1 = [
'HASH(0x1b542a8)'
];
When it should be printing
$VAR1 = [
['foo2', 'foo1']
];
Since foo2 has 1 zip and foo1 has 0 zip.

Answer 1

%HoH is declared as a hash, but is defined as a hashreference. Use parentheses (...) instead of braces {...}.
You don't need to loop through the hash to sort it. Sort will take care of that.
if you sort {...} keys %HoH, then the special variables $a and $b represent the keys of %HoH as it performs the sort.
$a and $b are in reverse order because your expected result is in decreasing order. (Update: Oh I just noticed that you had that in the first place.)
The zip value in the nested hash is $HoH{$KEY}{'zip'}, which is what you should sort by.
use strict;
use warnings;
use Data::Dumper;
my %HoH = (
'foo1' => {
'bam' => 1,
'zip' => 0,
},
'foo2' => {
'bam' => 0,
'zip' => 1,
'boo' => 1
}
);
my #sorted = sort {$HoH{$b}{'zip'} <=> $HoH{$a}{'zip'}} keys %HoH;
print Dumper \#sorted;
Note that the result of this code will give you an array:
$VAR1 = [
'foo2',
'foo1'
];
... not a nested array:
$VAR1 = [
['foo2', 'foo1']
];