This chapter introduced you to the Set collection of Immutable.js. The fundamental feature of sets is that they don't allow duplicate values. By converting lists to sets, you can remove duplicate values. If you try adding a duplicate value to a set, it just won't get added.
One challenge with sets is that they're not indexed, which means that you can't rely on consistent iteration behavior. The answer to this is to use ordered sets, which are capable of preserving the insertion order of values.
In the next chapter, you'll learn about comparing collections.
