Keith Elliot is an in-depth tutorials on understanding the 3 Swift Collection Types Arrays, Sets, and Dictionaries.
In the tutorials Keith provides a nice guide on how you can create and use the different types, and how you can use them to help improve your current classes.
You can find the tutorial in 3 different parts:
Part 1 – Understanding and using Arrays and Sets
Part 2 – Using Arrays and Sets and understanding dictionaries
Part 3 – Making Best Use of Arrays, Sets, and Dictionaries in Your Classes
Great guides for those getting started with collection types in Swift.