distinctBy but with last element

[ckosmowski]

I am currently evaluating vavr as a replacement for Java 8 Streams. While processing batches of events we always want to keep the last value unique by some key. The semantics would be the same as

.reverse()
.dicstinctBy(e -> e.getSomeKey())
.reverse()

i think.

But i do think that this comes with performance hits. To achieve this we are using a LinkedHashMap where we put elements one after the other with their generated keys and afterwards get the .values() again from that map which will now contain only the last elements of each key.

Would you consider adding "distinctByLast" or as we call it "keepLast" ?

[pivovarit]

That sounds like a good idea :) I'd lean towards a new distinctByKeepLast method for the sake of backward compatibility. We could target 0.11 and 1.0

[sam-chakrabarty]

I'd love to pick this issue up as my first contribution towards the repository. I'll put up a working PR for review over the next few days.

[pivovarit]

@sam-chakrabarty sure, it's yours :)

[sam-chakrabarty]

I'm targeting all implementations of Seq. Does that accurately capture the requirements of this issue?

[pivovarit]

No, this applies to all Traversables -> you need to add a method to Traversable interface called distinctByKeepLast and then implement them

[sam-chakrabarty]

I have taken a stab at solving this problem and have pushed out a PR here.

Please let me know if you have any questions or feedback.

[pivovarit]

This was implemented and will be a part of v0.11.0 :)