HASH可以splice么？

bulletming

我们知道splice删除数组一个eliment的时候，可以将eliment占用内存释放，而delete却不可以，那么有什么办法对hash数组作splice么？

除了先将hash转换为array的方法外！

另外我只想splice一个eliment，而不想清空整个hash数组

awake

Hash的数据结构需要使用splice delete吗？

ulmer

Hi,

SPLICING:
Hash has no original order by keys like an array. that means no first or last like an
array element pushed in a sequence.
So remove a key/value from a hash must be explicitly to say delete($hash{keyname}),
or use keys %hash and sort keys if possible, and you know that last key (sorted list) is
which you want to remove, then you can use splicing.


#############################################
SLICEING
Hash slice used to modify hash'svalues: format: @hash = @hash { KEY_LIST};

%tomAndJerry = (cat=>Tom, mouse=>Jerry);
# using hash slice to get values
@catAndMouse = @tomAndJerry{'cat', 'mouse'};
# @catAndMouse returns Tom, Jerry

# using hash slice to modifing hash value
@tomAndJerry{'cat', 'mouse'} = ('goofie', 'mikie');
# set value from key 'cat' as undef:
@tomAndJerry{'cat'} = ();    # same as $tomAndJerry{'cat'} = undef;
# hash tomAndJerry remains still 2 keys.

# using delete to remove hash's key/value paar and hash's keys will reduced.
delete $tomAndJerry{'cat'};
# hash tomAndJerry contained only moues/Jerry.


regards, ulmer

[ 本帖最后由 ulmer 于 2006-10-16 23:36 编辑 ]

bulletming

i think the func delete  will not remove the pair of key and value, a slot will be left when delete a element!

谁知道怎么去跟踪perl使用内存的情况呢？

ulmer

原帖由 bulletming 于 2006-10-17 00:19 发表
i think the func delete  will not remove the pair of key and value, a slot will be left when delete a element!

谁知道怎么去跟踪perl使用内存的情况呢？

Why not?! if say delete $tomAndJerry{'cat'}, what's happend %tomAndJerry?
If say $tomAndJerry{'cat'} = undef, what's happend %tomAndJerry?

try this:
use Data::Dumper;
%disney = ('cat'=>'Tom', 'mouse' => 'Jerry', dog=>'goofie');
delete $disney{'cat'};
$disney{'dog'} = '';
print Dumper(\%disney);

bulletming

1. #! /usr/local/bin/perl
   
2. 
   
3. my %test = (aaa => '123',bbb => '234',ccc=> '345');
   
4. 
   
5. print \$test{aaa}." key is aaa value is ".$test{aaa}."\n";
   
6. print \$test{bbb}." key is bbb value is ".$test{bbb}."\n";
   
7. print \$test{ccc}." key is ccc value is ".$test{ccc}."\n";
   
8. 
   
9. delete($test{bbb});
   
10. 
    
11. print \$test{aaa}." key is aaa value is ".$test{aaa}."\n";
    
12. print \$test{ccc}." key is ccc value is ".$test{ccc}."\n";
    
13. 
    
14. $test{ddd} = '999';
    
15. 
    
16. print \$test{aaa}." key is aaa value is ".$test{aaa}."\n";
    
17. print \$test{bbb}." key is bbb value is ".$test{bbb}."\n";
    
18. print \$test{ccc}." key is ccc value is ".$test{ccc}."\n";
    
19. print \$test{ddd}." key is ddd value is ".$test{ddd}."\n";

复制代码

结果：
root@ldapm # ./spli_hash.pl
SCALAR(0x1163f0) key is aaa value is 123
SCALAR(0x116504) key is bbb value is 234
SCALAR(0x116d20) key is ccc value is 345
SCALAR(0x1163f0) key is aaa value is 123
SCALAR(0x116d20) key is ccc value is 345
SCALAR(0x1163f0) key is aaa value is 123
SCALAR(0x11630c) key is bbb value is
SCALAR(0x116d20) key is ccc value is 345
SCALAR(0x116504) key is ddd value is 999

上边例子中说明了delete bbb之后,再增加一个ddd的key，它使用了原先bbb的内存空间。
我不知道是否可以说明这个问题！

等会，我作一个非常大的hash数组，看delete之后，是否prstat看到的内存会减少！

bulletming

谢谢！ ulmer!

Data:umper很好用！

flw

Perl 的 hash 空间是自动维护的，这没有什么好说的。

aaronvox

undef可以吗？

chinaseen

use Data:umper;
%disney = ('cat'=>'Tom', 'mouse' => 'Jerry', dog=>'goofie');
delete $disney{'cat'};
undef $disney{'dog'};
print Dumper(\%disney);
显示的结果为:
$VAR1 = {
          'dog' => undef,
          'mouse' => 'Jerry'
        };
不知道是否为楼上的所想要的结果!