如何优化Perl中的二维哈希遍历？

Question

我有哈希哈希%signal_db.一个典型的元素是:$signal_db{$cycle}{$key}.有10,000个信号和10,000个密钥.

有没有办法优化(按时)这段代码:

foreach my $cycle (sort numerically keys %signal_db) {
    foreach my $key (sort keys %{$signal_db{$cycle}}) {
        print $signal_db{$cycle}{$key}.$key."\n";
    }
}

元素必须以与我的代码相同的顺序打印.

Answer 1

两个微优化:映射内部哈希而不是常量解除引用和缓冲而不是常量打印.可以使用替代存储格式摆脱排序,测试两种变体.结果:

               Rate     original         try3  alternative alternative2
original     46.1/s           --         -12%         -21%         -32%
try3         52.6/s          14%           --         -10%         -22%
alternative  58.6/s          27%          11%           --         -13%
alternative2 67.5/s          46%          28%          15%           --

结论:

最好使用预先存储的存储格式,但没有C win可能在100%之内(在我的测试数据集上).提供的有关数据的信息表明,外部哈希中的键几乎是连续的数字,所以这就要求数组.

脚本:

#!/usr/bin/env perl

use strict; use warnings;
use Benchmark qw/timethese cmpthese/;

my %signal_db = map { $_ => {} } 1..1000;
%$_ = map { $_ => $_ } 'a'..'z' foreach values %signal_db;

my @signal_db = map { { cycle => $_ } } 1..1000;
$_->{'samples'} = { map { $_ => $_ } 'a'..'z' } foreach @signal_db;

my @signal_db1 = map { $_ => [] } 1..1000;
@$_ = map { $_ => $_ } 'a'..'z' foreach grep ref $_, @signal_db1;

use Sort::Key qw(nsort);

sub numerically { $a <=> $b }

my $result = cmpthese( -2, {
    'original' => sub {
        open my $out, '>', 'tmp.out';
        foreach my $cycle (sort numerically keys %signal_db) {
            foreach my $key (sort keys %{$signal_db{$cycle}}) {
                print $out $signal_db{$cycle}{$key}.$key."\n";
            }
        }
    },
    'try3' => sub {
        open my $out, '>', 'tmp.out';
        foreach my $cycle (map $signal_db{$_}, sort numerically keys %signal_db) {
            my $tmp = '';
            foreach my $key (sort keys %$cycle) {
                $tmp .= $cycle->{$key}.$key."\n";
            }
            print $out $tmp;
        }
    },
    'alternative' => sub {
        open my $out, '>', 'tmp.out';
        foreach my $cycle (map $_->{'samples'}, @signal_db) {
            my $tmp = '';
            foreach my $key (sort keys %$cycle) {
                $tmp .= $cycle->{$key}.$key."\n";
            }
            print $out $tmp;
        }
    },
    'alternative2' => sub {
        open my $out, '>', 'tmp.out';
        foreach my $cycle (grep ref $_, @signal_db1) {
            my $tmp = '';
            foreach (my $i = 0; $i < @$cycle; $i+=2) {
                $tmp .= $cycle->[$i+1].$cycle->[$i]."\n";
            }
            print $out $tmp;
        }
    },
} );