Here's how to get all of the elements of an array but the last n without knowing the length of the array.

I had the need the other day to find all but the last 2 elements of the array. You can use ranges pretty easily to do this but in my circumstance, I was in a chain of method calls and didn't want to create a local variable just to do this. The answer is simple:

                  #Get the last 2
                  n = 2
                  [1, 2, 3, 4, 5, 6][0..-n - 1] #You can use the .. range syntax if you offset by 1.
                  [1, 2, 3, 4, 5, 6][0...-n]    #Or you can use ... syntax to forgo the offset.
                  

It's easy to forget all these little convenience methods that Ruby affords. While I found out how to do this, I also remembered that last takes an optional argument so you can concisely take the last n elements like so:

                  [1,2,3,4,5,6].last(2)