Issue #19787 has been updated by joshuay03 (Joshua Young).
Is `.map { ... }.uniq` such a very frequent idiom?
I work on a Rails codebase and it's most commonly used to iterate through foreign keys
/ associated records and get the unique values (quite often in tests). That's the only
real frequent use case I've come across, but I would say that outside of that,
it's not an uncommon chaining pattern either.
`.uniq_map { ... }` is not as concise as `.map { ...
}.uniq`.
I'm a bit mixed on this point. I see where you're coming from, and I think the
same argument can be made about `#flat_map` and `#filter_map`. But it follows a similar
naming pattern where the alternative method is in the name, so I personally feel like
it's it's equally as concise?
I would also like to point out that with `#uniq_map`, you don't need to read all the
way to `.uniq` before inferring the output. This might help when the body of the `#map` is
quite complex, but you could argue that this is a code quality / style problem...
```
some_array.map do |item|
if some_condition
some_method(item)
else
some_other_method(item)
end
end.uniq
# vs
some_array.uniq_map do |item|
if some_condition
some_method(item)
else
some_other_method(item)
end
end
```
Scala doesn't seem to provide `uniqMap`.
Sorry, this is the first Ruby issue I've created or being involved with, so I'm
not sure why this was pointed out. Is this a usual consideration for new features?
Considering the above, I think the motivation is too
weak to provide `uniq_map`.
Your points are very valid, and I appreciate the response. What is the usual process for
deciding on whether or not to accept a feature?
----------------------------------------
Feature #19787: Add Enumerable#uniq_map, Enumerable::Lazy#uniq_map, Array#uniq_map and
Array#uniq_map!
https://bugs.ruby-lang.org/issues/19787#change-104016
* Author: joshuay03 (Joshua Young)
* Status: Open
* Priority: Normal
----------------------------------------
I would like to propose a collection of new methods, `Enumerable#uniq_map`,
`Enumerable::Lazy#uniq_map`, `Array#uniq_map` and `Array#uniq_map!`.
TL;DR: It's a drop in replacement for `.map { ... }.uniq`, with (hopefully) better
performance.
I've quite often had to map over an array and get its unique elements. It occurred to
me when doing so recently that Ruby doesn't have a short form method for doing that,
similar to how `.flat_map { ... }` replaces `.map { ... }.flatten` and `.filter_map { ...
}` replaces `.map { ... }.compact` (with minor differences). I think these new methods
could be beneficial both in terms of better performance and writing more succinct code.
I've got a draft PR up with some initial benchmarks in the description:
https://github.com/ruby/ruby/pull/8140.
--
https://bugs.ruby-lang.org/