RStudio is a formidable IDE to work with and offers an environment to seamlessly work with multiple languages beyond R. It is especially convenient for tasks involving frequent visualisation of data frames and plots, and for use with Shiny app development.
However, the text (i.e code) editing capabalities are still significantly lacking compared to the likes of Emacs and Vim. Besides this, it does not offer a seamless interface integrating task, time management and multi-language programming environments to the extent available within Org-mode via Emacs.
Lubridate - introductory technical paper This paper (Grolemund and Wickham) offers a good introduction and comparison between using lubridate and not using it, as well as several examples of using the library. It also offers some case studies which can serve as useful drill exercises.
Importing multiple excel sheets from multiple excel files This is one approach to importing multiple sheets from multiple excel files into a list of tibbles.
List of course certificates completed on platforms like DataCamp, DataQuest, EdX etc.