Update Lecture Day 3 and Interactive Session 3 for smaller conceptual jumps

[ryoliver]

Some of the introduction to for loops seems overly complicated.

The first example directly steps through vector elements, instead of iterating by position. And then we learn how to iterate by position. Personally, I think the first approach is harder to break into steps to show students, so it might be easier to go straight to the indexing approach. Especially because we introduce indexing at the end of the previous day

Approach 1:

Approach 2:

[ryoliver]

In the interactive session, it would be helpful to include code that shows how to build a for loop. In class, I showed students how I start writing for loops "from the inside out" (i.e. writing the body of the for loop for just one element and then generalizing). It would be helpful to build this directly into the materials, instead of just showing them the final solution.

[ryoliver]

The second lecture and final materials in the end of day interactive session introduce dplyr functions. It's nice to make the conceptual link to for loops, but we haven't formally introduced tidy syntax etc, so it feels like too much. It might be better to reinforce the current concepts and just flag that this connects to the material in the second week (as opposed to actually coding it)