Creating lesson on csv read write

This lesson should be finished and ready for review. I removed the inline tables from the end of the lesson, as these were meant to show the same thing as the figures that I was having trouble embedding (but that JB successfully embedded).
Could you please provide the answer to the challenge below? You can put it in a chunk and set the option `include=FALSE` so that none of the code or output is shown.

On the challenge itself, is there a better way to motivate this challenge? I don't think we want to discourage the practice of being able to re-run your code. In fact that is one of the benefits of a reproducible approach. If you find some unexpected behavior, you can fix it, restart your R session, and then re-source the code. Maybe you could motivate it as, "We want to keep it as a factor for some other operations we want to perform, so try to perform the replacement while keeping it as a factor."