Paul King commented on GROOVY-4606:

Given that we now have methods like {{DGM#toUnique(List, Comparator)}} and you 
can use {{Comparator.naturalOrder()}} to avoid coercion, should we close this 
issue or apply it as a small performance boost when using {{unique}}? I think 
it would belong inside the private {{uniqueItems}} method these days.

> Exteremely bad performance of .unique() and .unique {closure}
> -------------------------------------------------------------
>                 Key: GROOVY-4606
>                 URL: https://issues.apache.org/jira/browse/GROOVY-4606
>             Project: Groovy
>          Issue Type: Bug
>          Components: groovy-jdk
>    Affects Versions: 1.7.5
>            Reporter: Maxym Mykhalchuk
>            Priority: Major
>         Attachments: UniqueMath.java
> DefaultGroovyMethods.unique has two inner loops, so its complexity is O(n^2)
> Practically it means that it starts taking ages on collections with 1000 or 
> more elements.
> Simply adding elements to a linked hash set would get O(n*log n) performance.
> Will develop my own unique implementation after New Year, and will attach it 
> here

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