Labels and titles in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this plot title code?

Consider the following R code that creates a simple plot with a title and axis labels. What will be the title of the plot when this code runs?

R Programming

plot(1:5, 1:5, main = "My Plot Title", xlab = "X Axis", ylab = "Y Axis")
title(main = "Overridden Title")

A Overridden Title

B X Axis

C Y Axis

D My Plot Title

💡 Hint

The title() function can override the main title set in plot().

The plot() function sets the initial main title to "My Plot Title". The subsequent title() call with main = "Overridden Title" replaces the main title on the plot.

❓ Predict Output

intermediate

What label appears on the x-axis?

What label will appear on the x-axis after running this R code?

R Programming

barplot(1:3, names.arg = c("A", "B", "C"), xlab = "Category")

A A, B, C

B Category

C 1, 2, 3

D No label

💡 Hint

xlab sets the label for the x-axis, names.arg sets the names for bars.

The xlab argument sets the label for the x-axis, so "Category" will appear as the x-axis label. The names.arg argument labels each bar but does not change the axis label.

🔧 Debug

advanced

Why does this plot title not appear?

This R code is intended to add a title to the plot, but no title appears. What is the cause?

R Programming

plot(1:10, 1:10)
title(main = "My Title", sub = "Subtitle")
title(xlab = "X Label")

A The xlab argument in title() does not set the x-axis label; it must be set in plot().

B The title() function cannot add subtitles; sub is ignored.

C The plot() function must include main argument to show any title.

D The title() function calls overwrite each other, so only the last call works.

💡 Hint

Check which arguments title() accepts and which must be set in plot().

The title() function accepts main, sub, and line arguments but does not accept xlab or ylab. Axis labels must be set in the plot() function or with separate axis labeling functions.

🧠 Conceptual

advanced

How to add multiple lines in a plot title?

Which option correctly adds a multi-line main title to a plot in R?

A plot(1:5, main = "Line 1\nLine 2")

B plot(1:5, main = c("Line 1", "Line 2"))

C plot(1:5); title(main = "Line 1\nLine 2")

D plot(1:5); title(main = c("Line 1", "Line 2"))

💡 Hint

Use newline characters in strings or multiple calls to title().

The newline character \n inside a string works in title() to create multi-line titles. The main argument in plot() does not interpret \n properly for multi-line titles, so using title() after plot() is the correct approach.

❓ Predict Output

expert

What is the output of this label and title code?

What will be the main title and axis labels of the plot after running this R code?

R Programming

plot(1:3, 1:3, main = "First Title", xlab = "X1", ylab = "Y1")
title(main = "Second Title", xlab = "X2")
title(ylab = "Y2")

A Main title: Second Title; X-axis label: X1; Y-axis label: Y1

B Main title: First Title; X-axis label: X1; Y-axis label: Y1

C Main title: First Title; X-axis label: X2; Y-axis label: Y2

D Main title: Second Title; X-axis label: X2; Y-axis label: Y2

💡 Hint

title() can override main and sub titles but not axis labels; check which labels are updated.

The first title() call overrides the main title. However, title() does not accept xlab or ylab arguments, so axis labels remain as set in plot(). The second title() call with ylab is ignored. So the final labels are main = "Second Title", xlab = "X1", ylab = "Y1".

Practice

1. What is the purpose of using main in an R plot?

easy

A. To add a main title to the plot

B. To label the x-axis

C. To label the y-axis

D. To change the plot color

Solution

1. Step 1: Understand the role of main in plotting

   The main argument in R's plot function is used to set the main title of the graph.

2. Step 2: Differentiate from axis labels

   xlab and ylab are used for x-axis and y-axis labels respectively, not main.

3. Final Answer:

   To add a main title to the plot -> Option A

4. Quick Check:

   main = main title [OK]

Hint: Remember: main = title, xlab = x-axis, ylab = y-axis [OK]

Common Mistakes:

• Confusing main with axis labels
• Using main to change colors
• Omitting labels entirely

2. Which of the following is the correct syntax to add a y-axis label "Height" in an R plot?

easy

A. plot(x, y, xlab = "Height")

B. plot(x, y, ylab = "Height")

C. plot(x, y, main = "Height")

D. plot(x, y, label = "Height")

Solution

1. Step 1: Identify the argument for y-axis label

   In R, ylab is used to set the label for the y-axis.

2. Step 2: Check the syntax correctness

   The syntax plot(x, y, ylab = "Height") correctly assigns "Height" as the y-axis label.

3. Final Answer:

   plot(x, y, ylab = "Height") -> Option B

4. Quick Check:

   ylab = y-axis label [OK]

Hint: Use ylab for y-axis label inside plot() [OK]

Common Mistakes:

• Using main instead of ylab for y-axis label
• Using xlab for y-axis label
• Using a non-existent label argument

3. What will be the main title of the plot after running this code?

plot(1:5, 1:5, main = "Sales Over Time", xlab = "Month", ylab = "Sales")

medium

A. Month

B. No title

C. Sales

D. Sales Over Time

Solution

1. Step 1: Identify the main title argument

   The argument main = "Sales Over Time" sets the main title of the plot.

2. Step 2: Confirm other labels are axis labels

   xlab = "Month" and ylab = "Sales" set the x-axis and y-axis labels, not the main title.

3. Final Answer:

   Sales Over Time -> Option D

4. Quick Check:

   main = "Sales Over Time" [OK]

Hint: main sets the plot title, not axis labels [OK]

Common Mistakes:

• Confusing xlab or ylab as main title
• Ignoring the main argument
• Assuming no title if not obvious

4. Identify the error in this R plot code:

plot(x, y, main = "Data", xlabel = "Time", ylab = "Value")

medium

A. The argument 'xlabel' is incorrect; it should be 'xlab'

B. The argument 'main' should be 'title'

C. The argument 'ylab' should be 'ylabel'

D. There is no error in the code

Solution

1. Step 1: Check the axis label arguments

   In R, the correct argument for x-axis label is xlab, not xlabel.

2. Step 2: Verify other arguments

   main is correct for the title, and ylab is correct for y-axis label.

3. Final Answer:

   The argument 'xlabel' is incorrect; it should be 'xlab' -> Option A

4. Quick Check:

   Use xlab, not xlabel [OK]

Hint: Use xlab and ylab, not xlabel or ylabel [OK]

Common Mistakes:

• Using xlabel instead of xlab
• Using ylabel instead of ylab
• Changing main to title incorrectly

5. You want to create a plot with the main title "Temperature Trends", x-axis label "Year", and y-axis label "Temperature (°C)". Which code correctly achieves this?

hard

A. plot(years, temps, main = "Temperature Trends", xlab = "Year")

B. plot(years, temps, title = "Temperature Trends", xlabel = "Year", ylabel = "Temperature (°C)")

C. plot(years, temps, main = "Temperature Trends", xlab = "Year", ylab = "Temperature (°C)")

D. plot(years, temps, main = "Temperature Trends", xlabel = "Year", ylab = "Temperature (°C)")

Solution

1. Step 1: Use correct arguments for labels and title

   The correct arguments are main for the title, xlab for the x-axis label, and ylab for the y-axis label.

2. Step 2: Check each option for correctness

   plot(years, temps, main = "Temperature Trends", xlab = "Year", ylab = "Temperature (°C)") uses all correct arguments. plot(years, temps, title = "Temperature Trends", xlabel = "Year", ylabel = "Temperature (°C)") uses incorrect argument names. plot(years, temps, main = "Temperature Trends", xlabel = "Year", ylab = "Temperature (°C)") uses incorrect xlabel. plot(years, temps, main = "Temperature Trends", xlab = "Year") misses the y-axis label.

3. Final Answer:

   plot(years, temps, main = "Temperature Trends", xlab = "Year", ylab = "Temperature (°C)") -> Option C

4. Quick Check:

   main, xlab, ylab = correct labels [OK]

Hint: Always use main, xlab, ylab for titles and axis labels [OK]

Common Mistakes:

• Using title instead of main
• Using xlabel or ylabel instead of xlab or ylab
• Forgetting one of the labels