我有一个散列哈希％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.
解决方法
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;
}
},} );