不想对条目进行排序.
使用它也不会保留顺序
foreach my $val (keys %hash) {
...
}
解决方法
默认情况下,Perl 5中的哈希是无序的.您可以使用
tie和
Tie::IxHash来覆盖此行为.不过要警告,有一个表现打击和其他考虑(例如,这个订单不会保留在副本中).
#!/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";
}
更好的选择可能是使用数组或散列哈希：
#!/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";
}
至于表现,以下是一个基准的结果：
IndexedOO: a,b,c,d,e,f
HashOrdered: a,f
IxHashOO: a,f
hash: f,a,d
hoh_pis: a,f
IxHash: a,f
hoh: a,f
Indexed: a,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% --
从这里我们可以看到,如果您不需要使用Hash :: Ordered就可以像普通哈希(即绑定的哈希)那样运行.
这是基准：
#!/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++,perfect_insert_sort \%h;
},IxHash => sub {
my $i;
tie my %h,"Tie::IxHash";
%h = map { $_ => $i++ } @keys;
return join ",Indexed => sub {
my $i;
tie my %h,"Tie::Hash::Indexed";
%h = map { $_ => $i++ } @keys;
return join ",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;