Recently-added Scala cheat sheets, tutorials, syntax, and examples alvin June 17, 2018 - 6:10pm

As I try to organize things a bit around here, here’s a list of some tutorials I’ve written lately about the Scala collections classes:

Scala Seq class: methods, examples, and syntax

This page contains a large collection of examples of how to use the methods on the Scala Seq class.

Important note about Seq, IndexedSeq, and LinearSeq

As an important note, I use Seq in the following examples to keep things simple, but in your code you should be more precise and use IndexedSeq or LinearSeq where appropriate. As the Seq class Scaladoc states:

Scala: How to append and prepend items to Vector and Seq alvin April 27, 2018 - 1:01pm
Table of Contents1 - Solution2 - Example data3 - Append a single item4 - Append multiple elements5 - Prepend a single item6 - Prepend multiple elements7 - Seq works just like Vector8 - How to remember the method names9 - A possible problem

Scala FAQ: How do I append or prepend one or more elements to a Vector or Seq class?

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To append or prepend one or more elements to a Vector or Seq, use these methods:

How to get multiple, unique, random elements from a list of elements

One thing I never thought about before is that if you need to get multiple, unique, random elements from a list of elements, one solution to the problem is to shuffle the list and then take as many elements as you want/need. For instance, if you want three unique, random elements from a list of integers in Scala, you can do this:

scala> val list = List(1,2,3,4,5,1,2,3,4,5)
list: List[Int] = List(1, 2, 3, 4, 5, 1, 2, 3, 4, 5)

scala> val uniq = list.distinct
uniq: List[Int] = List(1, 2, 3, 4, 5)

scala> val shuffled = scala.util.Random.shuffle(uniq)
shuffled: List[Int] = List(1, 4, 5, 2, 3)

scala> val firstThree = shuffled.take(3)
firstThree: List[Int] = List(1, 4, 5)

As that solution shows, you start with a simple list; get the unique/distinct elements from the list; shuffle those elements to create a new list; then take the first three elements from the shuffled list. That’s probably not a great solution for huge lists, but for many simple lists it’s a way to get multiple random elements from the list.

Methods on the Scala collections classes, organized by category

When I wrote the Scala Cookbook, I gave each recipe and then each chapter my full attention. I thought that if I wrote each recipe as well as possible, and included important recipes in each chapter, well, I wanted each chapter to be worth the price of the entire book. That was my goal.

As a result of this effort -- and perhaps to the chagrin of my editor -- the Scala collections chapters ended up being 130 pages in length.