Themes and theme customization in R Programming - Mini Project: Build & Apply

Themes and Theme Customization in R

📖 Scenario: You are creating a simple bar chart to show sales data for different products. You want to make the chart look nicer by changing the theme colors and text styles.

🎯 Goal: Build a bar chart using ggplot2 with a customized theme that changes the background color, text size, and axis titles.

📋 What You'll Learn

Create a data frame called sales_data with products and their sales numbers

Create a variable called base_size to set the base font size for the theme

Use ggplot() to create a bar chart with geom_bar() using sales_data

Customize the plot theme using theme() to change background color, axis title size, and text color

Print the final plot

💡 Why This Matters

🌍 Real World

Customizing themes helps make charts clearer and more attractive for presentations and reports.

💼 Career

Data analysts and scientists often need to adjust chart styles to match company branding or improve readability.

1

Create the sales data

Create a data frame called sales_data with these exact entries: Product as 'A', 'B', 'C' and Sales as 30, 45, 25.

R Programming

# Create the sales_data data frame with Product and Sales columns
# Your code here

Hint

Use data.frame() with Product = c('A', 'B', 'C') and Sales = c(30, 45, 25).

2

Set the base font size

Create a variable called base_size and set it to 14 to control the font size in the theme.

R Programming

sales_data <- data.frame(Product = c('A', 'B', 'C'), Sales = c(30, 45, 25))
# Create base_size variable and set it to 14
# Your code here

Hint

Just assign 14 to base_size.

3

Create the bar chart with customized theme

Use ggplot() with sales_data, map Product to x and Sales to y, add geom_bar(stat = 'identity'), and customize the theme with theme() to set panel.background to light gray, axis title text size to base_size, and axis text color to blue.

R Programming

sales_data <- data.frame(Product = c('A', 'B', 'C'), Sales = c(30, 45, 25))
base_size <- 14

# Create ggplot bar chart with customized theme
# Your code here

Hint

Use theme() to customize background and text styles.

4

Display the customized plot

Print the plot stored in the variable plot to display the customized bar chart.

R Programming

library(ggplot2)
sales_data <- data.frame(Product = c('A', 'B', 'C'), Sales = c(30, 45, 25))
base_size <- 14

plot <- ggplot(sales_data, aes(x = Product, y = Sales)) +
  geom_bar(stat = 'identity') +
  theme(
    panel.background = element_rect(fill = 'lightgray'),
    axis.title = element_text(size = base_size),
    axis.text = element_text(color = 'blue')
  )

# Print the plot
# Your code here

Hint

Use print(plot) to show the plot.

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()