This is a list of methods from Ruby's Array, Hash, and Enumerable that I find useful and have used a lot. It is by no means an complete list so just think of it as a starting point. (BTW, Enumerable is a mixin and not a class but both Array and Hash include it they both have Enumerable methods avaliable to them.)
In preperation for this week and the upcoming week make sure you are understand how to sort and filter each of these data structures. Read the documentation on these methods and play with them in IRB.
After you are familiar with each one of these methods try out a few more. Read through the method lists of each and read up on any that you think might be useful or ones you can't tell what they do. One "lifehack" I have heard of is setting one of these pages as your new-tab homepage on your browser. They every so often you might pick up a new method.
As will all of EDA we will be building on top of you knowledge as you go. These methods are the foundations that will make your life easier later on.
Hey Samson - none of these links seem to be going to the actual method, just to a broken link at Ruby-doc.org....