By far my favorite feature of lodash is the sortby function, in which instead of providing a custom comparator as most std libraries’ sort() function offers, provides a way to substitute a simpler object for the comparator to chew on. If your comparator needs to go beyond a couple nested conditionals, to actual data transform or grabbing locks, then that nasty little logn term in the runtime can take your sort from using 20% of the time budget for an expensive operation to taking 120%. Especially when you consider the memory bandwidth sloshing around L3 or the main memory bus to do the full table scan logn times.

I think the world would be better off if this wasn’t in a third part library in a single programming language. Iirc Ruby is the only language I know with it as a built-in.

Rust's slice of T [T] provides [T]::sort_by_cached_key which is a stable IPN sort which lets you provide a key transform callable f, which it will call at most once for each item to be sorted, sorting by comparing the (cached) results from that callable.

https://doc.rust-lang.org/std/primitive.slice.html#method.so...

However ..._by_cached_key is not provided for Rust's unstable sort because the unstable sort doesn't require an allocator and necessarily a cache does need an allocator.

This is well known in Perl as the Schwartz transform