Themes and theme customization in R Programming - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to apply a minimal theme to a ggplot.

R Programming

library(ggplot2)
ggplot(mtcars, aes(x=wt, y=mpg)) + geom_point() + [1]()

Drag options to blanks, or click blank then click option'

Atheme_classic

Btheme_minimal

Ctheme_dark

Dtheme_bw

Attempts:

3 left

💡 Hint

Common Mistakes

Using a theme function that changes the plot style but is not minimal.

Forgetting the parentheses after the theme function.

The theme_minimal() function applies a minimalistic theme to the plot, removing background grids and decorations.

2fill in blank

medium

Complete the code to change the base font size of a ggplot theme to 16.

R Programming

ggplot(mtcars, aes(x=wt, y=mpg)) + geom_point() + theme_minimal(base_size = [1])

Drag options to blanks, or click blank then click option'

A16

B10

C12

D20

Attempts:

3 left

💡 Hint

Common Mistakes

Using a smaller font size like 10 or 12 when the goal is to increase size.

Forgetting to assign the value to base_size.

Setting base_size = 16 changes the base font size of the theme to 16 points.

3fill in blank

hard

Fix the error in the code to set the plot background color to light blue.

R Programming

ggplot(mtcars, aes(x=wt, y=mpg)) + geom_point() + theme(plot.background = element_rect(fill = [1]))

Drag options to blanks, or click blank then click option'

Alight blue

Bblue light

C#lightblue

Dlightblue

Attempts:

3 left

💡 Hint

Common Mistakes

Using color names with spaces like 'light blue'.

Adding '#' before color names that are not hex codes.

The color name must be a single word string like 'lightblue'. Spaces or incorrect formats cause errors.

4fill in blank

hard

Fill both blanks to customize axis text color and size.

R Programming

ggplot(mtcars, aes(x=wt, y=mpg)) + geom_point() + theme(axis.text.x = element_text(color = [1], size = [2]))

Drag options to blanks, or click blank then click option'

A"red"

B14

C12

D"blue"

Attempts:

3 left

💡 Hint

Common Mistakes

Using color without quotes.

Choosing a smaller size when the goal is to increase text size.

Setting color = "red" changes the x-axis text color to red, and size = 14 makes the text larger.

5fill in blank

hard

Fill all three blanks to create a custom theme with green panel background, no grid lines, and bold axis titles.

R Programming

ggplot(mtcars, aes(x=wt, y=mpg)) + geom_point() + theme(panel.background = element_rect(fill = [1]), panel.grid.major = [2], axis.title = element_text(face = [3]))

Drag options to blanks, or click blank then click option'

A"green"

Belement_blank()

C"bold"

D"italic"

Attempts:

3 left

💡 Hint

Common Mistakes

Using color names without quotes.

Using incorrect functions to remove grid lines.

Using 'italic' instead of 'bold' for axis titles.

Setting fill = "green" colors the panel background green, element_blank() removes major grid lines, and face = "bold" makes axis titles bold.

Practice

1. What is the main purpose of using theme() in ggplot2?

easy

A. To customize the appearance of the plot, like colors and fonts

B. To add data points to the plot

C. To change the data source of the plot

D. To save the plot as an image file

Solution

1. Step 1: Understand the role of theme()

   The theme() function in ggplot2 is used to change how the plot looks, such as colors, fonts, and backgrounds.

2. Step 2: Differentiate from other plot functions

   Functions like adding data points or saving files are not related to theme(). It only changes the visual style.

3. Final Answer:

   To customize the appearance of the plot, like colors and fonts -> Option A

4. Quick Check:

   Theme controls appearance = D [OK]

Hint: Remember: theme() changes look, not data or saving [OK]

Common Mistakes:

• Confusing theme() with adding data layers
• Thinking theme() saves the plot
• Assuming theme() changes data source

2. Which of the following is the correct way to change the plot background to white using theme()?

easy

A. theme(panel.background = element_rect(fill = "white"))

B. theme(background = element_white())

C. theme(bgcolor = "white")

D. theme(background_color = "white")

Solution

1. Step 1: Recall correct syntax for background color

   In ggplot2, the plot background is changed by setting panel.background to element_rect() with a fill color.

2. Step 2: Identify the correct option

   theme(panel.background = element_rect(fill = "white")) uses panel.background = element_rect(fill = "white"), which is the correct syntax. Other options use incorrect argument names or functions.

3. Final Answer:

   theme(panel.background = element_rect(fill = "white")) -> Option A

4. Quick Check:

   panel.background + element_rect(fill) = A [OK]

Hint: Use panel.background with element_rect(fill=) for backgrounds [OK]

Common Mistakes:

• Using wrong argument names like background or bgcolor
• Using element_white() which does not exist
• Setting background_color instead of panel.background

3. What will be the effect of this code on a ggplot object p?

p + theme(axis.text.x = element_text(angle = 45, hjust = 1))

medium

A. Remove x-axis text labels

B. Rotate y-axis text labels 45 degrees and align them to the left

C. Change x-axis text color to red

D. Rotate x-axis text labels 45 degrees and align them to the right

Solution

1. Step 1: Understand the theme modification

   The code modifies axis.text.x, which means the x-axis text labels. It sets their angle to 45 degrees and horizontal justification to 1 (right aligned).

2. Step 2: Interpret the visual effect

   This will rotate the x-axis labels diagonally and align them to the right side, improving readability for long labels.

3. Final Answer:

   Rotate x-axis text labels 45 degrees and align them to the right -> Option D

4. Quick Check:

   axis.text.x + angle 45 + hjust 1 = A [OK]

Hint: axis.text.x controls x labels; angle rotates, hjust aligns [OK]

Common Mistakes:

• Confusing x-axis with y-axis text
• Thinking it changes color instead of rotation
• Assuming it removes labels

4. Identify the error in this theme customization code:

theme(axis.title = element_text(size = 14, face = "bold"))

medium

A. face argument cannot be "bold"

B. axis.title should be axis.title.x or axis.title.y

C. size argument must be a string, not a number

D. element_text() cannot be used inside theme()

Solution

1. Step 1: Check valid theme element names

   In ggplot2, axis titles are specified separately as axis.title.x and axis.title.y. There is no general axis.title element.

2. Step 2: Verify other arguments

   The face argument accepts "bold" correctly, size is numeric as expected, and element_text() is valid inside theme().

3. Final Answer:

   axis.title should be axis.title.x or axis.title.y -> Option B

4. Quick Check:

   axis.title invalid, use axis.title.x/y = B [OK]

Hint: Use axis.title.x or axis.title.y, not axis.title [OK]

Common Mistakes:

• Using axis.title instead of axis.title.x or axis.title.y
• Thinking face="bold" is invalid
• Confusing size type requirements

5. You want to create a custom theme that sets the plot title font size to 20, makes axis text blue, and removes the legend background. Which of the following theme codes achieves this correctly?

hard

A. theme(plot.title.size = 20, axis.text.color = "blue", legend.background = NULL)

B. theme(title.size = 20, axis.text.color = "blue", legend.bg = element_blank())

C. theme(plot.title = element_text(size = 20), axis.text = element_text(color = "blue"), legend.background = element_blank())

D. theme(plot.title = element_text(fontsize = 20), axis.text = element_text(col = "blue"), legend.background = element_blank())

Solution

1. Step 1: Check correct element names and arguments

   The plot title font size is set by plot.title = element_text(size = 20). Axis text color is set by axis.text = element_text(color = "blue"). Legend background removal uses legend.background = element_blank().

2. Step 2: Identify incorrect options

   Options A, B, and D use invalid element names or arguments. A uses plot.title.size and axis.text.color directly, B uses title.size and legend.bg, D uses fontsize and col.

3. Final Answer:

   theme(plot.title = element_text(size = 20), axis.text = element_text(color = "blue"), legend.background = element_blank()) -> Option C

4. Quick Check:

   Correct element names and arguments = C [OK]

Hint: Use exact element names and argument names in theme() [OK]

Common Mistakes:

• Using wrong element names like title.size
• Using fontsize instead of size
• Using col instead of color
• Setting legend.background to NULL instead of element_blank()