[jira] [Commented] (COLLECTIONS-479) An Order Statistic Tree

["Thomas Neidhart (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/COLLECTIONS-479?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13708980#comment-13708980 ] 

Thomas Neidhart commented on COLLECTIONS-479:
---------------------------------------------

Thanks for the suggestion and the patch.
Ideally, the new class should be embedded into an existing collection type and in this case I guess a Set would be appropriate. To include a new feature into collections we would also need unit tests that fit into the test framework.

Looking at the proposed feature itself, I think it could be solved by using the already existing TreeList. We just need a method to find the insertion point by traversing the tree in sort order. The corresponding index is stored in the AVLTree nodes, which is then used to provide the select / rank functionality:

 * select(index) = get(index)
 * rank(obj) = indexOf(obj)
                
> An Order Statistic Tree
> -----------------------
>
>                 Key: COLLECTIONS-479
>                 URL: https://issues.apache.org/jira/browse/COLLECTIONS-479
>             Project: Commons Collections
>          Issue Type: New Feature
>            Reporter: Ajo Fod
>            Priority: Minor
>         Attachments: NodeExistsException.java, RedBlackBST.java
>
>
> An order statistic tree http://en.wikipedia.org/wiki/Order_statistic_tree provides two useful properties. The ability to rank arbitrary keys relative to keys existing in the tree AND the ability to retrieve elements from the tree with the given rank.
> This can be used to find the percentile rank of a key for example.
> This functionality is not yet provided yet by any of the major libraries AFAIK.

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