Introduction to regular expressions in R presented at the Columbia Political Science Graduate Student Methods Workshop on March 1st, 2019. The repository can be found here, and you can find the presentation here.
Introduction to R presented for incoming Columbia Political Science PhD students, on August 27th, 2019. I made the presentation with learnr, so it also functions as an online tutorial, which you can find here, though the Shiny app might not work at times when I don't have it running.