The "little extra work" includes keeping the resulting array sorted. Otherwise, there's no way to detect which is currently the smallest value, and which one needs replacing. Only $n items need to be printed, and if $n is small enough, I can imagine that perl's built-in sort will do well enough. As the data is sorted, you can try insert a new value at the appropriate place yourself, but the overhead of doing this in pure perl might not be worth it.

Also, personally, I'd prefer to keep more than $n items if there's a tie for the lowest value of those to keep. For example, if you need the top 3 values and the top 5 hash values are (1, 2, 4, 4, 5), I'd actually keep the top 4: (1, 2, 4, 4). So here's some code that implements that. I also added lots of reporting code, showing exactly what's going on.
Feel free to "optimize" it. 

my %HASH;
foreach('AA' .. 'ZZ') {
    $HASH{$_} = 1 + int rand 1000;
}

my $keep = 20;
my @top;
if(scalar keys %HASH <= $keep) {
    # You actually need to show them all.
    @top = sort { $b->[1] <=> $a->[1] } map [$_, $HASH{$_}], keys %HAS
+H;
} else {
    my $threshold;
    while(my($key, $value) = each %HASH) {
        if(@top < $keep) {
            printf "Adding %s => %d\n", $key => $value;
            push @top, [$key, $value];
            $threshold = $value if !defined $threshold or $value > $th
+reshold;
        } elsif($value > $threshold) {
            @top = sort { $b->[1] <=> $a->[1] } @top, [$key, $value];
            printf "Inserting %s => %d\n", $key => $value;
            $threshold = $top[$keep-1][1];
            printf "New threshold: %d\n", $threshold;
            while($top[-1][1] < $threshold) {
                printf "Popping %s => %d\n", @{$top[-1]};
                pop @top;
            }
            printf "Keeping %d items\n", scalar @top;
        } elsif($value == $threshold) {
            printf "Adding %s => %d\n", $key => $value;
            push @top, [$key, $value];
        }
    }
}

use Data::Dumper;
$Data::Dumper::Terse = 1;
print Dumper \@top;

[download]

In reply to Re: Re: *Fastest* way to print a hash sorted by value by bart
in thread *Fastest* way to print a hash sorted by value by smellysocks

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