Hi all, I realize that many of you may still feel confused by the material from Module 4 and the corresponding questions in Assignment 2. To hopefully clarify this confusion, I've assembled a supplement to Module 4, which I've posted on the CLE, under the section for Module 4. The first section summarizes techniques for subsetting data. I've changed the ordering of the presentation (relative to how the material was presented in the slides), in the hopes of clarifying the material. The second two sections provide further information on the data argument and the with() function. I hope this added material helps. As always, please don't hesitate to get in touch if you are feeling lost.