Steven Sanderson talks data types:
Imagine your data as a diverse collection of individuals. Some might be numbers (like age or weight), while others might be text (like names or addresses). These different categories are called data types, and R recognizes several key ones:
Click through for that list. It’s a bit different from what you’d expect if you come at this from a SQL or C-based programming language background. But they all make good sense when you remember that R is a domain-specific language for statistics, so it’s going to emphasize the things that make the most sense for statisticians and data scientists.