Box plots and violin plots in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a basic boxplot in R

What will be the output of this R code snippet?

R Programming

data <- c(5, 7, 8, 5, 6, 9, 10, 12, 7, 6)
boxplot(data, main = "Simple Boxplot")

A An error because boxplot requires a data frame

B A boxplot showing median around 7 with whiskers extending roughly from 5 to 12

C A scatter plot of data points against their index

D A histogram of the data with bars representing frequency

💡 Hint

Boxplots summarize data distribution with median and quartiles.

The boxplot function in R creates a box showing the median and quartiles. The whiskers extend to the min and max within 1.5 times the interquartile range. The data vector is valid input.

🧠 Conceptual

intermediate

Difference between boxplot and violin plot

Which statement correctly describes the difference between a boxplot and a violin plot?

A A violin plot is a 3D version of a boxplot with added colors.

B Both plots show the same information but use different colors.

C A boxplot shows individual data points, while a violin plot only shows the median.

D A boxplot shows summary statistics like median and quartiles, while a violin plot shows the data distribution shape using a kernel density estimate.

💡 Hint

Think about what each plot reveals about the data.

Boxplots summarize data with median, quartiles, and outliers. Violin plots add a smooth shape showing the full distribution density.

🔧 Debug

advanced

Identify the error in violin plot code

What error will this R code produce?

R Programming

library(ggplot2)
data <- data.frame(group = rep(c('A', 'B'), each = 10), value = c(rnorm(10), rnorm(10, 2)))
ggplot(data, aes(x = group, y = value)) + geom_violin() + geom_boxplot()

A No error; the code runs and produces a violin plot with boxplot overlay

B Error: geom_violin requires a numeric x aesthetic, but group is a factor

C Error: ggplot2 not loaded properly

D Error: geom_boxplot cannot be added after geom_violin

💡 Hint

Check if the code syntax and library usage are correct.

The code loads ggplot2, creates a data frame with groups and values, then plots violin and boxplot layers. This is valid and runs without error.

❓ Predict Output

advanced

Output of customized boxplot with notch

What does the following R code produce?

R Programming

set.seed(123)
data <- rnorm(50)
boxplot(data, notch = TRUE, col = "lightblue", main = "Notched Boxplot")

A A boxplot with a notch around the median indicating confidence interval, colored light blue

B A histogram of data colored light blue

C A boxplot without notch and default color

D An error because notch requires a data frame

💡 Hint

Notches show confidence intervals around the median.

The notch parameter adds a notch shape around the median to indicate a confidence interval. The color changes the box fill.

❓ Predict Output

expert

Combined violin and boxplot with jittered points

What will be the output of this R code?

R Programming

library(ggplot2)
set.seed(42)
data <- data.frame(category = rep(c('X', 'Y'), each = 20), value = c(rnorm(20), rnorm(20, 1)))
ggplot(data, aes(x = category, y = value)) + geom_violin(trim = FALSE, fill = "pink") + geom_boxplot(width = 0.1, fill = "white") + geom_jitter(width = 0.15, alpha = 0.5)

A Only jittered points plotted without violin or boxplot

B A violin plot trimmed at tails with no boxplot or points

C A violin plot with full tails (not trimmed), white narrow boxplots inside, and jittered points scattered horizontally

D Error: geom_jitter requires a numeric x aesthetic

💡 Hint

Look at each geom layer and their parameters.

The code creates a violin plot with tails shown (trim=FALSE), overlays a narrow white boxplot, and adds jittered points with some transparency.