ggplot() and aes() basics in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this ggplot code?

Consider the following R code using ggplot2. What will be the main visual element shown?

R Programming

library(ggplot2)
data <- data.frame(x = 1:5, y = c(3, 5, 2, 8, 7))
ggplot(data, aes(x = x, y = y)) + geom_point()

A A bar chart with bars at x positions 1 to 5 with heights 3 to 7

B A line plot connecting points (1,3), (2,5), (3,2), (4,8), (5,7)

C A scatter plot with points at coordinates (1,3), (2,5), (3,2), (4,8), (5,7)

D An empty plot with no points or lines

💡 Hint

Look at the geom_point() function. It adds points to the plot.

The geom_point() function creates a scatter plot by placing points at the (x, y) coordinates specified in aes(). So the plot shows points at the given data coordinates.

❓ Predict Output

intermediate

What happens if you swap x and y in aes()?

Given the same data, what will this code produce?

R Programming

library(ggplot2)
data <- data.frame(x = 1:5, y = c(3, 5, 2, 8, 7))
ggplot(data, aes(x = y, y = x)) + geom_point()

A A scatter plot with points at coordinates (3,1), (5,2), (2,3), (8,4), (7,5)

B An error because x and y are swapped

C A line plot connecting points (3,1), (5,2), (2,3), (8,4), (7,5)

D A scatter plot with points at coordinates (1,3), (2,5), (3,2), (4,8), (5,7)

💡 Hint

Swapping x and y in aes() changes the axes.

Swapping x and y means the horizontal axis shows the original y values and the vertical axis shows the original x values. The points are plotted accordingly.

🧠 Conceptual

advanced

Which option correctly maps color to a variable?

In ggplot2, how do you map the color of points to a variable group in the data?

A ggplot(data, aes(x = x, y = y)) + geom_point(aes(color = group))

B ggplot(data, aes(x = x, y = y)) + geom_point(color = group)

C ggplot(data, aes(x = x, y = y, color = group)) + geom_point()

D ggplot(data, aes(x = x, y = y)) + geom_point(color = "group")

💡 Hint

Mapping aesthetics inside aes() links them to data variables.

To map color to a variable, you include color = group inside aes() in ggplot(). Option A also works by placing aes(color = group) inside geom_point() since aesthetics merge, but option C is the standard way using the global aes().

🔧 Debug

advanced

Why does this ggplot code produce an error?

Look at this code snippet. Why does it cause an error?

R Programming

library(ggplot2)
data <- data.frame(x = 1:3, y = c(4, 5, 6))
ggplot(data, aes(x = x, y = y)) + geom_point(aes(color = z))

A Because variable 'z' does not exist in the data frame

B Because color cannot be mapped inside geom_point()

C Because aes() must be outside ggplot()

D Because geom_point() requires a size aesthetic

💡 Hint

Check if all variables used in aes() exist in the data.

The error occurs because z is not a column in the data frame. ggplot2 cannot map color to a variable that does not exist.

❓ Predict Output

expert

How many points will be plotted here?

Given this code, how many points will appear in the plot?

R Programming

library(ggplot2)
data <- data.frame(x = c(1, 2, 2, 3), y = c(4, 5, 5, 6))
ggplot(data, aes(x = x, y = y)) + geom_point()

A 3 points, duplicates are automatically removed

B An error due to duplicate points

C 5 points, because ggplot adds one extra point

D 4 points, including duplicates at (2,5)

💡 Hint

ggplot2 plots all rows; duplicates are not removed automatically.

ggplot2 plots one point per row in the data frame. Duplicate points appear multiple times. So all 4 points, including duplicates, are plotted.