The reverse isn't reversing the sort, it's reversing the order of the elements of the list returned by the sliced sort.

Check the parenthesis.

??
swapping $a and $b and dropping reverse gives me 34, 56 ?

Are you sure? On my box this is the same...


#!/usr/local/bin/perl
$num=5;
my %hash = ('1' => 12, '2' => 34, '3' => 56, '4' => 2);
@values = reverse ((sort {$a <=> $b} values %hash)[0..--$num]);
print @values, "\n";
$num=5;
@values = (sort {$b <=> $a} values %hash)[0..--$num];
print @values, "\n";


----->
/home/jonathan> z   
5634122
5634122
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"We are all prompted by the same motives, all deceived by the same fallacies, all animated by hope, obstructed by danger, entangled by desire, and seduced by pleasure." - Samuel Johnson

#!/usr/bin/perl -w

require 5;
use strict;
use Benchmark;
use vars qw( $hash_size %random_hash $num );

$num = 2;
$hash_size = 1000;

# Generate random hash
my $r;
for ($r=1; $r<=$hash_size; $r++) {
    $random_hash{"$r"} = int(rand(1000));
}


sub Lowest(\%) {
    my $hashref = shift;
    my %hash = %{$hashref};
    my $position;
    my $current;
    my @lowest;
    for ($position=0; $position<$num; $position++) {
        my $min;
        my $elem;
        foreach $elem (keys %hash) {
            if (!defined($min) || $hash{$elem} < $min) {
                $min = $hash{$elem};
                $current = $elem;
            }
        }
        $lowest[$position] = $min;
        delete $hash{$current};
        last if !(%hash);
    }
    return @lowest;
}

sub Sort(\%) {
    my $hashref = shift;
    my %hash = %{$hashref};
    my @lowest = (sort {$b <=> $a} values %hash)[0..--$num];
    return @lowest;
}


timethese (
  -20,
    {
        'Method 1' => 'Lowest(%random_hash)',
        'Method 2' => 'Sort(%random_hash)'
    });

exit;
[download]

abowley@lave:~$ ./lowest.pl
Benchmark: running Method 1, Method 2, each for at least 20 CPU second
+s...
  Method 1: 25 wallclock secs (19.80 usr +  0.21 sys = 20.01 CPU) @ 42
+.53/s (n=851)
  Method 2: 25 wallclock secs (20.33 usr +  0.22 sys = 20.55 CPU) @ 43
+.16/s (n=887)
[download]