1. it’s better to use accessor methods, i.e. coef() rather than [["coefficients"]]] or $coefficients, whenever possible
2. always best to use names in original data set (shorten them by renaming up-front if necessary); rather than

a <- dd$x
b <- dd$y
c <- dd$z
lm(c~b+a)

do

lm(z~y+x, data=dd)

Always try to keep variable names meaningful (but also short enough for convenience)

3. always start a clean R session when working on your code. Before submitting, make sure it all runs by clicking on the “Source” button. Do not start your code with rm(list=ls()) ! See here

4. It’s fine to use functions from other packages, but you must indicate where they come from! It’s helpful to include all of your library() specifications at the top of your R script (not in the middle where they are first used), so users can see that they will need to install them. Please do not include install.packages() commands in your R script (unless they’re commented out)

5. You can spell-check an Rmarkdown file easily in RStudio; if you are submitting homework as an R file with embedded comments, you can temporarily tell RStudio to treat your file as a text file (click on the file type indicator at the bottom right of the script window and select Text file; click on the spell-check “ABC” icon (you’ll have to “ignore” a certain number of R commands, variable names, etc.); click on the file type indicator to switch the type back to R script).