One of the most useful data structures in Computer Science is the hash table. I’ve been using them for my entire career and have implemented close to a hundred instances in several languages. That’s not as necessary these days as most modern languages—and some not so modern languages such as Lisp—have them as a built-in data type.
Happily, Elisp is one of those languages. If you’re not already familiar with the Emacs implementation of hash tables, you can get the details in the manual (of course) but Xah Lee has an excellent overview that will get you up and running quickly. There’s not much to learn and hash tables are incredibly useful when you need a fast look up data structure so give Lee’s post a look and see if they can be useful to you.