Performance ordered dictionary vs normal dictionary

[Navkirat Singh]

On 29-Jul-2010, at 9:36 AM, sturlamolden wrote:

> On 29 Jul, 03:47, Navkirat Singh <navkir... at gmail.com> wrote:
> 
>> I was wondering what would be better to do some medium to heavy book keeping in memory - Ordered Dictionary or a plain simple Dictionary object??
> 
> It depends on the problem. A dictionary is a hash table. An ordered
> dictionary is a binary search tree (BST). Those are different data
> structures.
> 
> The main things to note is that:
> 
> - Access is best-case O(1) for the hash table and O(log n) for the
> BST.
> 
> - Worst case behavior is for access is O(n) for both. The pathologic
> conditions are excessive collisions (hash) or an unbalanced tree
> (BST). In pathologic cases they both converge towards a linked list.
> 
> - Searches are only meaningful for == and != for a hash table, but BST
> searches are also meaningful for >, <, <=, and >=. For this reason,
> databases are often implemented as BSTs.
> 
> - A BST can be more friendly to cache than a hash table, particularly
> when they are large. (Remember that O(1) can be slower than O(log n).
> Big-O only says how run-time scales with n.)
> 
> That said, I have not compared ordered dicts with normal dicts, as I
> still use 2.6.
> 
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> -- 
> http://mail.python.org/mailman/listinfo/python-list


Thanks for the insight. I am still in the thinking stage, so will let you know as and when I get down to implementation of my idea.

Thanks for your time. : )

Regards,
Nav