When I started to use the data.table package I was primarily using it to aggregate. I had read about data.table and its blazing speed compared to the other options from base or the plyr package especially with large amounts of data. As an example, I remember calculating averages or percentages while at Saint Paul Public Schools and while the calculations were running would walk away for 5 minutes to wait for them to finish.
My first statistical software package I used as an undergrad was SPSS. I was fortunate during my senior year at Luther College to be initially introduced to R. I did not realize it at the time (except for the pretty graphics) that this was the start of something big for me. Fast forward a year to graduate school at the University of Minnesota and the majority of my program was again using SPSS.
This past summer when the twin cities R user group was starting to get back up and running, I offered to present on some R related things that I was working on. One thing I was working on was a part of my last post. In a response to discussing this during a meeting, I was posed with the problem of how to do this with a markdown table. I replied I was unsure how to do this directly with R, but it could likely be possible.