In this hour, we focused on two structures that store “multi-mode” data (that is, data containing more than one data type). First, we looked at lists, which allow us to store any number of objects of varying modes. Then, we looked at data frames as a special “type” of list that stores rectangular datasets in an effective manner.
Although lists are very powerful structures, when we import data into R (which you’ll see in Hour 10, “Importing and Exporting”), it will be stored as a data frame. Therefore, you need to be very comfortable manipulating this structure in particular. You should practice the syntax relating the subscripting of data frames using square brackets and the $ symbol, because this is a fundamental skill useful across all R tasks.