Consider adding `classify`.

[Andreas Abel]

This cannot be done efficiently.  I'd extend the equivalence relation to 
a total order and then use sort and group.

-1 to adding to the standard libraries.  How about publishing this as a 
(well discoverable) package on hackage and see how popular it gets?

On 2020-08-20 19:59, Ignat Insarov wrote:
> Hello.
> 
> There has been [a question on Stack Overflow][1] asking for a way to group a
> list by an equivalence relation. Several answers were proposed over time, and I
> too [have offered a variant][2]. [I also wrote a benchmark.][3]
> 
> I propose that the function be added to the standard libraries.
> 
> [1]: https://stackoverflow.com/q/8262179
> [2]: https://stackoverflow.com/a/57761458
> [3]: https://github.com/kindaro/classify-benchmark.git
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