Sort Perl hash from largest to smallest

Question

I am looking at an example found here: http://perlmeme.org/tutorials/sort_function.html

And it gives this code to sort a hash based on each key's value:

# Using <=> instead of cmp because of the numbers
    foreach my $fruit (sort {$data{$a} <=> $data{$b}} keys %data) {
        print $fruit . ": " . $data{$fruit} . "\n";
    }

This code I do not fully understand, but when I experiment with it, it sorts from lowest to highest. How can I flip it to sort from highest to lowest?

Solution 1

Swap $a and $b:

foreach my $fruit (sort {$data{$b} <=> $data{$a}} keys %data) {

Solution 2

Just use reverse sort instead of sort.

foreach my $fruit (reverse sort keys %data) { ...

Comments

[Mark Reed]

That works, but sorting and then reversing the list is less efficient than just swapping the sense of the comparison in the first place.

[toolic]

@MarkReed: This seems to claim reverse is not less efficient: search.cpan.org/~thaljef/Perl-Critic-1.117/lib/Perl/Critic/…

[Ωmega]

@MarkReed: reverse is more efficient and more readable code.

[chepner]

@toolic: Interesting, did not know that. I wonder if the optimization extends to comparing $data{$a} and $data{$b}, instead of just $a and $b.