Github user superruzafa created a very helpful visual guide to scala functions that I look at regularly. Neat design, simple, helpful.
https://superruzafa.github.io/visual-scala-reference//
Alvin Alexander is the author of the Scala Cookbook and other books on Scala and functional programming. He also has a vast library of little articles, code examples and excerpts from his books on his personal website. If you are programming Scala or learning to do so you’ve probably already stumbled upon it.