不想对条目进行排序。
使用这种方法也不能保留顺序。
foreach my $val (keys %hash) {
...
}
在Perl 5中,默认情况下哈希表是无序的。你可以使用tie
和Tie::IxHash
来覆盖这种行为。但要注意,这样做会导致性能下降和其他考虑因素(例如将不保留顺序的副本)。
#!/usr/bin/perl
use strict;
use warnings;
use Tie::IxHash;
tie my %hash, "Tie::IxHash"
or die "could not tie %hash";
$hash{one} = 1;
$hash{two} = 2;
$hash{three} = 3;
for my $k (keys %hash) {
print "$k $hash{$k}\n";
}
一个更好的选择可能是使用数组或哈希表:
#!/usr/bin/perl
use strict;
use warnings;
my %hash;
$hash{one} = { data => 1, order => 1 };
$hash{three} = { data => 3, order => 2 };
$hash{two} = { data => 2, order => 3 };
for my $k (sort { $hash{$a}{order} <=> $hash{$b}{order} } keys %hash) {
print "$k $hash{$k}{data}\n";
}
就性能而言,这里是一个基准测试的结果:
IndexedOO: a, b, c, d, e, f
HashOrdered: a, b, c, d, e, f
IxHashOO: a, b, c, d, e, f
hash: f, e, a, c, b, d
hoh_pis: a, b, c, d, e, f
IxHash: a, b, c, d, e, f
hoh: a, b, c, d, e, f
Indexed: a, b, c, d, e, f
Rate IxHash hoh Indexed IxHashOO IndexedOO hoh_pis HashOrdered hash
IxHash 261/s -- -18% -26% -48% -54% -57% -66% -80%
hoh 316/s 21% -- -10% -37% -44% -48% -59% -75%
Indexed 353/s 35% 12% -- -29% -38% -42% -55% -72%
IxHashOO 499/s 91% 58% 41% -- -12% -18% -36% -61%
IndexedOO 569/s 118% 80% 61% 14% -- -7% -27% -56%
hoh_pis 611/s 134% 93% 73% 22% 7% -- -21% -52%
HashOrdered 778/s 198% 146% 120% 56% 37% 27% -- -39%
hash 1279/s 391% 305% 262% 156% 125% 109% 64% --
从这里我们可以看出,如果您不需要它像正常哈希表(即绑定哈希表)一样运行,那么使用Hash::Ordered是最好的选择。
以下是基准测试结果:
#!/usr/bin/perl
use strict;
use warnings;
use Tie::IxHash;
use Tie::Hash::Indexed;
use Hash::Ordered;
use Benchmark;
#this is O(n) instead of O(n log n) or worse
sub perfect_insert_sort {
my $h = shift;
my @k;
for my $k (keys %$h) {
$k[$h->{$k}{order}] = $k;
}
return @k;
}
my @keys = qw/a b c d e f/;
my %subs = (
hash => sub {
my $i;
my %h = map { $_ => $i++ } @keys;
return join ", ", keys %h;
},
hoh => sub {
my $i;
my $order;
my %h = map {
$_ => { data => $i++, order => $order++ }
} @keys;
return join ", ", sort { $h{$a}{order} <=> $h{$b}{order} }
keys %h;
},
hoh_pis => sub {
my $i;
my $order;
my %h = map {
$_ => { data => $i++, order => $order++ }
} @keys;
return join ", ", perfect_insert_sort \%h;
},
IxHash => sub {
my $i;
tie my %h, "Tie::IxHash";
%h = map { $_ => $i++ } @keys;
return join ", ", keys %h;
},
Indexed => sub {
my $i;
tie my %h, "Tie::Hash::Indexed";
%h = map { $_ => $i++ } @keys;
return join ", ", keys %h;
},
IxHashOO => sub {
my $i;
my $o = tie my %h, "Tie::IxHash",
map { $_ => $i++ } @keys;
return join ", ", $o->Keys;
},
IndexedOO => sub {
my $i;
my $o = tie my %h, "Tie::Hash::Indexed",
map { $_ => $i++ } @keys;
my @k = my $k = $o->FIRSTKEY;
while ($k = $o->NEXTKEY($k)) {
push @k, $k;
}
return join ", ", @k;
},
HashOrdered => sub {
my $i;
my $oh = Hash::Ordered->new( map { $_ => $i++ } @keys );
return join ", ", $oh->keys;
},
);
for my $sub (keys %subs) {
print "$sub: ", $subs{$sub}(), "\n";
}
@keys = 1 .. 1_000;
Benchmark::cmpthese -2, \%subs;
Tie::Hash::Indexed
,我需要去看一下。 - Chas. Owens$obj = tied %hash; $obj->STORE($key, $value)
。完整的接口在Tie::Hash文档中。 - SchwernHash::Ordered
添加基准测试吗?https://metacpan.org/pod/Hash::Ordered 谢谢。 - stenlytw