Data Analysis

In-Class Exercise 2

Yu-You Liou

Shih Chien University

2026-08-03

Question 1

Start from the basic scatterplot of displ vs hwy from the mpg dataset. Map the class variable to the colour aesthetic inside aes(), so that each vehicle class is drawn in a different colour.

Write one sentence identifying which class of car tends to have the worst highway fuel economy for its engine size, judging from the colours.

Question 2

Instead of colour, split the same scatterplot into small multiples: use facet_wrap(~class) to create one panel per vehicle class.

Write one sentence comparing this facetted plot to the coloured plot from Question 1 — which one makes it easier to see the pattern within a single class, and why?

Question 3

Return to the single-panel scatterplot of displ vs hwy and add a smooth trend layer with geom_smooth() on top of geom_point(). Then make a second version using geom_smooth(method = "lm").

Write one sentence explaining what the default (curved) smoother reveals about cars with very large engines that the straight line misses.

Submission

Complete your answers in the official template from the Problem sets page (author = your student ID only; keep the UUID chunk). Knit to PDF, name it ex2-[StudentID].pdf, and upload it to the course pCloud folder before midnight of the following week.