Trim indexing section / work on transition to functions

[sstevens2]

No description provided.

[sstevens2]

Keep c(), colon, and seq?

[sstevens2]

Maybe introduce seq as a function (and arguments) and then to vectors and to df - @ChristinaLK has more detail here

[BajczA475]

I might be able to help with streamlining the Intro R lesson as well. I don't want to overcommit and then not be able to actually get the things done though. All we're looking for is just a "tighter" lesson, yes? If so, once we have goals, this shouldn't be too bad. The one thing I would stress is making sure we only teach them what they need to directly apply in later lessons (unless more general R familiarity is a goal of the lesson, which I would be fine with, but we would need to define that concretely).