Lesson 1 Exercise Questions: ggplot2 basics

These exercise questions should be attempted after completing Lesson 1: Introduction to ggplot2 for R Data Visualization.

Q1: What geoms would you use to draw each of the following named plots?

a. Scatterplot  
b. Line chart   
c. Histogram   
d. Bar chart   
e. Pie chart

(Question taken from https://ggplot2-book.org/individual-geoms.html.)

Q1: Solution

a. geom_point
b. geom_line
c. geom_histogram
d. geom_bar
c. geom_bar with coord_polar

Q2. We will use the mpg data set for the remainder of the questions. Use ?mpg to learn more about these data. Visualize highway miles per gallon (hwy) by the class of car using a box plot.

Q2: Solution

library(ggplot2)

ggplot(mpg)+
  geom_boxplot(aes(class,hwy))

Q3. Using the plot from Q2, fill each box with color by class.

Q3: Solution

ggplot(mpg)+
  geom_boxplot(aes(class,hwy,fill=class))

Q4. Challenge Question: Using the plot from Q3, reorder the boxes by the median of hwy. Hint: See fct_reorder() from forcats.

Q4: Solution

library(forcats)
ggplot(mpg)+
  geom_boxplot(aes(fct_reorder(factor(class),hwy,median),hwy,fill=class))

Q5. Visualize highway miles per gallon (hwy) by the class of car using a violin plot.

Q5: Solution

ggplot(mpg)+
  geom_violin(aes(class,hwy))

Q6. Visualize a cars engine size in liters (displ) versus fuel efficiency on the hwy (hwy) using a scatter plot.

Q6: Solution

ggplot(mpg) +
  geom_point(aes(displ,hwy))

Q7. Using the plot generated in Q6, fit a smooth line (loess) to the data. Color the points by car class.

Q7: Solution

ggplot(mpg) +
  geom_point(aes(displ,hwy,color=class))+
  geom_smooth(aes(displ,hwy))
## `geom_smooth()` using method = 'loess' and formula = 'y ~ x'

Q8. Visualize a histogram of hwy and facet by year. What is bindwidith (See ?geom_histogram)? Explore the binwidth and color the bars red with a black outline.

Q8: Solution

ggplot(mpg)+
  geom_histogram(aes(hwy),fill="red",color="black", binwidth=5) +
  facet_wrap(~year)