1. What R command(s) would you use to remove null values from a dataset? 2. What R command can be used to install an additional R package? 3. What R function is used to encode a vector as a category? 4. What is a rug plot used for in a density plot? 5. An online retailer wants to study the purchase behaviors of its customers. Figure 3.27 shows the density plot of the purchase sizes (in dollars). What would be your recommendation to enhance the plot to detect more structures that otherwise might be missed?

Density 8e-04 6e-04 4e-04 2e-04 0e+00 0 2000 4000 6000 purchase size (dollars) 8000 10000