Themes and theme customization in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this ggplot2 theme customization?

Consider the following R code using ggplot2. What will be the color of the plot title?

R Programming

library(ggplot2)

p <- ggplot(mtcars, aes(x = wt, y = mpg)) +
  geom_point() +
  ggtitle("Car Data") +
  theme(plot.title = element_text(color = "blue"))

print(p)

A The plot title will be red.

B The plot title will be blue.

C The plot title will be invisible.

D The plot title will be black (default).

💡 Hint

Look at the theme() function and the element_text() color argument.

The theme() function changes the plot appearance. Here, plot.title = element_text(color = "blue") sets the title color to blue.

🧠 Conceptual

intermediate

Which theme element controls the background color of the plot panel?

In ggplot2, which theme element should you modify to change the background color inside the plotting area (where data points appear)?

A <code>panel.background</code>

B <code>panel.grid</code>

C <code>plot.background</code>

D <code>axis.text</code>

💡 Hint

Think about the area inside the axes where the data is drawn.

The panel.background controls the background of the plotting panel where data points are shown. plot.background controls the entire plot's background including titles and labels.

🔧 Debug

advanced

Why does this theme customization not change the axis text color?

Look at this code snippet:

library(ggplot2)

p <- ggplot(mtcars, aes(x = wt, y = mpg)) +
  geom_point() +
  theme(axis.text = element_text(color = "red"))

print(p)

Why does the axis text color remain black?

A Because <code>geom_point()</code> overrides the theme settings.

B Because <code>axis.text</code> is not a valid theme element; it should be <code>axis.text.x</code> or <code>axis.text.y</code>.

C Because the color argument should be <code>color</code> not <code>colour</code>.

D Because the theme must be added before <code>geom_point()</code>.

💡 Hint

Check the spelling of the color argument in element_text(): it should be color.

The element_text() function expects color = (American spelling). colour = is not recognized by ggplot2 theme elements, so the color does not change. Use color = "red".

📝 Syntax

advanced

Which option correctly sets the legend position to the bottom?

Choose the correct syntax to move the legend to the bottom of a ggplot2 plot.

A theme(legend.position = "bottom")

B theme(legend.position = bottom)

C theme(legend.position = bottom())

D theme(legend.position = c("bottom"))

💡 Hint

Legend position expects a string value.

The legend position must be a string like "bottom". Option A correctly uses quotes. Other options are invalid syntax or wrong types.

🚀 Application

expert

How many theme elements are changed by this custom theme?

Given this custom theme code, how many distinct theme elements are modified?

custom_theme <- theme(
  plot.title = element_text(size = 16, face = "bold"),
  axis.title.x = element_text(color = "darkgreen"),
  axis.title.y = element_text(color = "darkgreen"),
  panel.background = element_rect(fill = "lightyellow"),
  panel.grid.major = element_line(color = "gray"),
  panel.grid.minor = element_line(color = "lightgray"),
  legend.position = "top"
)

A 6

B 8

C 5

D 7

💡 Hint

Count each unique theme element name inside theme().

The theme modifies 7 elements: plot.title, axis.title.x, axis.title.y, panel.background, panel.grid.major, panel.grid.minor, and legend.position.