We should have access to [std::slice::group_by](https://doc.rust-lang.org/std/slice/struct.GroupBy.html) in a future version of Rust, and already have those through [itertools](https://docs.rs/itertools/latest/itertools/structs/struct.GroupBy.html). Does that change some of the algorithmic costs incurred by .sort() here?

[porcuquine]

          We should have access to [`std::slice::group_by`](https://doc.rust-lang.org/std/slice/struct.GroupBy.html) in a future version of Rust, and already have those through [itertools](https://docs.rs/itertools/latest/itertools/structs/struct.GroupBy.html). Does that change some of the algorithmic costs incurred by `.sort()` here?

Originally posted by @huitseeker in #1004 (comment)