blocks|key|245182|text|php数组基本上是哈希表。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|245183|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

php arrays ARE basically hash tables

blocks|key|1795467|text|在PHP中，关联数组被实现为哈希表，并带有一些额外的功能。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1795468|然而，从技术上讲，关联数组与哈希表并不完全相同--它只是部分地通过幕后的哈希表来实现。因为它的大多数实现都是哈希表，所以它可以完成哈希表所能做的一切--但它也可以做更多的事情。|1795469|例如，您可以使用For循环遍历关联数组，这是哈希表无法执行的。|1795470|因此，虽然它们是相似的，但关联数组实际上可以执行哈希表所能做的超集，因此它们不是完全相同的事情。把它看作是哈希表加上额外的功能。|offset|length|style|BOLD|1795471|代码示例：|1795472|使用关联数组作为哈希表|1795473|$favoriteColor+=+array();
$favoriteColor['bob']='blue';
$favoriteColor['Peter']='red';
$favoriteColor['Sally']='pink';
echo+'bob+likes:+'.$favoriteColor['bob']."\n";
echo+'Sally+likes:+'.$favoriteColor['Sally']."\n";
//output:+bob+likes+blue
//++++++++Sally+likes+pink|code-block|syntax|javascript|1795474|循环通过关联数组|1795475|$idTable=array();
$idTable['Tyler']=1;
$idTable['Bill']=20;
$idTable['Marc']=4;
//up+until+here,+we're+using+the+array+as+a+hashtable.

//now+we+loop+through+the+array+-+you+can't+do+this+with+a+hashtable:
foreach($idTable+as+$person=>$id)
++++echo+'id:+'.$id.'+%7C+person:+'.$person."\n";

//output:+id:+1+%7C+person:+Tyler
//++++++++id:+20+%7C+person:+Bill
//++++++++id:+4+%7C+person:+Marc|1795476|特别要注意的是，在第二个示例中，如何根据输入数组的顺序来维护每个元素的顺序(泰勒、Bill+)。这是关联数组和哈希表之间的一个主要区别。哈希表在它所持有的项之间不保持连接，而PHP关联数组则保持连接(您甚至可以对PHP关联数组进行排序)。|1795477|entityMap^0|0|0|0|V|2|0|0|0|B|0|0|0|8|0|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|13|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|14|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|15|8|@$H|16|I|17|J|K]]|9|@]|A|$]]|$1|L|3|M|5|6|7|18|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|19|8|@$H|1A|I|1B|J|K]]|9|@]|A|$]]|$1|P|3|Q|5|R|7|1C|8|@]|9|@]|A|$S|T]]|$1|U|3|V|5|6|7|1D|8|@$H|1E|I|1F|J|K]]|9|@]|A|$]]|$1|W|3|X|5|R|7|1G|8|@]|9|@]|A|$S|T]]|$1|Y|3|Z|5|6|7|1H|8|@]|9|@]|A|$]]|$1|10|3|-4|5|6|7|1I|8|@]|9|@]|A|$]]]|11|$]]

In PHP, associative arrays are implemented as hashtables, with a bit of extra functionality.

However technically speaking, an associative array is not identical to a hashtable - it's simply implemented in part with a hashtable behind the scenes. Because most of its implementation is a hashtable, it can do everything a hashtable can - but it can do more, too.

For example, you can loop through an associative array using a for loop, which you can't do with a hashtable.

So while they're similar, an associative array can actually do a superset of what a hashtable can do - so they're not exactly the same thing. Think of it as hashtables plus extra functionality.

Code examples:

Using an associative array as a hashtable:

<pre><code>$favoriteColor = array();
$favoriteColor['bob']='blue';
$favoriteColor['Peter']='red';
$favoriteColor['Sally']='pink';
echo 'bob likes: '.$favoriteColor['bob']."\n";
echo 'Sally likes: '.$favoriteColor['Sally']."\n";
//output: bob likes blue
// Sally likes pink
</code></pre>

Looping through an associative array:

<pre><code>$idTable=array();
$idTable['Tyler']=1;
$idTable['Bill']=20;
$idTable['Marc']=4;
//up until here, we're using the array as a hashtable.

//now we loop through the array - you can't do this with a hashtable:
foreach($idTable as $person=&gt;$id)
 echo 'id: '.$id.' | person: '.$person."\n";

//output: id: 1 | person: Tyler
// id: 20 | person: Bill
// id: 4 | person: Marc
</code></pre>

Note especially how in the second example, the order of each element is maintained (Tyler, Bill Marc) based on the order in which they were entered into the array. This is a major difference between associative arrays and hashtables. A hashtable maintains no connection between the items it holds, whereas a PHP associative array does (you can even sort a PHP associative array).

blocks|key|1441298|text|关联数组是一个数组，在该数组中，不按索引访问元素，而是按键访问元素。它的内部工作方式是特定于实现的(没有规则规定它必须如何工作)。关联数组可以通过哈希表实现(大多数实现都会这样做)，但也可以通过某种树结构或跳过列表来实现，或者该算法只对数组中的所有元素进行迭代，并查找匹配的键(这将非常慢，但它有效)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1441299|哈希表是一种存储数据的方法，其中值与键相关联，以及您打算在(通常几乎)恒定时间内找到键的值。这听起来与您对关联数组的期望完全一样，这就是为什么大多数时间哈希表都用于实现这些数组，但这不是强制性的。|1441300|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

An associative array is an array where you don't access elements by an index, but by a key. How this works internally is implementation specific (there is no rule how it must work). An associative array could be implemented by a hash table (most implementations will do that), but it could also be implemented by some sort of tree structure or a skip list or the algorithm just iterates over all elements in the array and looks for a key that matches (this would be awfully slow, but it works).

A hash table is a way how to store data where values are associated to keys and where you intend to find values for keys within a (usually almost) constant time. This sounds exactly like what you expect of an associative array, that's why most of the time hash tables are used for implementing those arrays, but that is not mandatory.

blocks|key|1795575|text|关联数组和哈希表的区别在于关联数组是数据类型，而哈希表是数据实现。显然，在许多当前的编程语言中，关联数组类型非常重要:+Perl、Python、PHP等。哈希表是实现关联数组的主要方法，但不是唯一的方法。关联数组是哈希表的主要用途，但并不是唯一的用途。所以这并不是说它们是相同的，但是如果您已经有了关联数组，那么您通常不应该担心它们之间的区别。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1795576|出于性能原因，重要的是要知道您喜欢的语言中的关联数组是以散列的形式实现的。对实现的开销有一些了解可能是很重要的。哈希表比线性数组使用的内存更慢，在C中可以看到它们。|1795577|Perl通过调用关联数组“散列”将这两个概念合并在一起。就像Perl的许多特性一样，它不是完全错误的，但它是草率的。|1795578|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

The difference between an associative array and a hash table is that an associative array is a data type, while a hash table is a data implementation. Obviously the associative array type is very important in many current programming languages: Perl, Python, PHP, etc. A hash table is the main way to implement an associative array, but not quite the only way. And associative arrays are the main use of hash tables, but not quite the only use. So it's not that they are the same, but if you already have associative arrays, then you usually shouldn't worry about the difference.

For performance reasons, it can be important to know that your associative arrays in your favorite language are implemented as hashes. And it can be important to have some idea of the overhead cost of that implementation. Hash tables are slower and use more memory than linear arrays as you see them in C.

Perl lumps the two concepts together by calling associative arrays "hashes". Like a number of features of Perl, it isn't quite wrong, but it's sloppy.

blocks|key|245320|text|PHP中的数组实际上是一个有序映射，而不是哈希表。map和hashtable之间的主要区别在于无法记住已添加的wich元素中的顺序。另一方面，哈希表比地图快得多。从map获取元素的复杂性是O(nlogn)，从hashtable获取元素的复杂性是O(1)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|245321|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

An array in PHP is actually an ordered map, not hashtable. Main difference between map and hashtable consists in inability to remember the order in wich elements have been added. On the other hand, hashtables are much faster than maps. Complexity of fetching an element from map is O(nlogn) and from hashtable is O(1).

Recently I have read about hash-tables in a very famous book "<a href="http://www.introductiontoalgorithms.com/" rel="noreferrer">Introduction to Algorithms</a>". I haven't used them in any real applications yet, but want to. But I don't know how to start. 
Can anyone give me some samples of using it, for example, how to realize a dictionary application (like ABBYY Lingvo) using hash-tables? 
And finally I would like to know what is the difference between hash-tables and associative arrays in PHP, I mean which technology should I use and in which situations? 
If I am wrong (I beg pardon) please correct me, because actually I am starting with hash-tables and I have just basic (theoretical) knowledge about them. 
Thanks a lot.

Hash tables VS associative arrays

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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最近，我在一本非常有名的书“”中读到了关于哈希表的文章。我还没有在任何真正的应用程序中使用它们，但我想使用。但我不知道怎么开始。有人能给我一些使用它的示例吗，例如，如何使用哈希表来实现字典应用程序(比如ABBYY )？最后，我想知道PHP中哈希表和关联数组之间的区别是什么，我的意思是我应该使用哪种技术，在什么情况下使用...

问哈希表与关联数组
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