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https://issues.apache.org/jira/browse/COLLECTIONS-479?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15148762#comment-15148762
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Rodion Efremov commented on COLLECTIONS-479:
--------------------------------------------

I am more or less done with a Set-implementation that provides methods get(int 
index) and indexOf(T element); both run in O(log N). See here: 
https://github.com/coderodde/OrderStatisticTree

However, if a Map is required, please tell me, should not take much time to 
refactor.

Best,
rodde

> 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
>             Fix For: 4.x
>
>         Attachments: COLLECTIONS-479.patch, 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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