Advanced Sorting in Perl

[Clive Bostock]

Hello.
I have a hash which I need sorting. Each record in the hash consists of a string with numbers separated by commas. For example ('2.1, 4.3, 2.5,...3.1').
I wish to sort my hash by the sum of the values. I wrote a function, sum_fields, to receive the string and return the total the values. However I was hoping to reference the subroutine / function like this:

for $key (sort { sum_fields{$csv{$b}} <=> sum_fields{$csv{$a}} } keys %csv)

However, Perl doesn't like this. I get:
Bareword found where operator expected at D:\Mydata\sandpit\awrcsv.pl line 548,
near "<=> sum_fields"
(Missing operator before sum_fields?)
Any ideas how best to achieve this? I am being lazy and trying to avoid loading my hash into a more complex hash structure which I could readily sort.
Thanks,
Clive

[miller]

You called your function, sum_fields using braces {} instead of parenthesis (). That's the cause of your error.

I personally would use the List::Util core library and a Schwartzian Transform:

use List::Util qw(sum);
 
use strict;
use warnings;
 
my %csv = (
    '2.1, 4.3, 2.5, 3.1' => 1,
    '2.1, 4.3, 2.5, 3.3' => 1,
    '2.1, 4.3, 2.5, 3.2' => 1,
);
 
for my $key (map {$_->[0]} sort {$b->[1] <=> $a->[1]} map {[$_, sum split ',', $_]} keys %csv) {
    print "$key\n";
}
 

- Miller