Scatter plots (geom_point) in R Programming - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of basic scatter plot code

What will be the output of this R code using ggplot2?

R Programming

library(ggplot2)
data <- data.frame(x = 1:5, y = c(2, 3, 5, 7, 11))
ggplot(data, aes(x = x, y = y)) + geom_point()

A An error because geom_point() requires a color aesthetic

B A line plot connecting points (1,2), (2,3), (3,5), (4,7), (5,11)

C A bar chart showing y values for x from 1 to 5

D A scatter plot with points at coordinates (1,2), (2,3), (3,5), (4,7), (5,11)

💡 Hint

geom_point() creates scatter plots by plotting points at given x and y coordinates.

The code uses ggplot2 to plot points at the specified x and y values. geom_point() adds points, not lines or bars.

🧠 Conceptual

intermediate

Understanding aesthetics in geom_point

Which option correctly describes the role of the aes() function inside ggplot() when creating a scatter plot with geom_point()?

A aes() defines how variables map to visual properties like x and y positions of points

B aes() sets the size of the plot window

C aes() adds titles and labels to the plot

D aes() changes the color of the plot background

💡 Hint

Think about what aes() does with data variables in ggplot2.

aes() maps data variables to visual aesthetics like x, y, color, size, shape, etc. It does not control plot size or labels.

🔧 Debug

advanced

Identify the error in this scatter plot code

What error will this R code produce?

R Programming

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

A Error: object 'color' not found

B SyntaxError: unexpected end of input due to missing closing parenthesis

C No error, plot will show blue points

D Error: geom_point() requires a size argument

💡 Hint

Check if all parentheses are properly closed.

The original code was missing a closing parenthesis after geom_point(color = "blue"), causing a syntax error. The corrected code includes the closing parenthesis.

❓ Predict Output

advanced

Effect of mapping color inside aes() vs outside

What is the difference in output between these two ggplot2 codes?

R Programming

library(ggplot2)
data <- data.frame(x = 1:4, y = c(2, 4, 6, 8), group = c('A', 'B', 'A', 'B'))

# Code 1:
ggplot(data, aes(x = x, y = y, color = group)) + geom_point()

# Code 2:
ggplot(data, aes(x = x, y = y)) + geom_point(color = 'red')

A Both codes color points by group

B Code 1 colors points by group; Code 2 colors all points red

C Code 1 colors all points red; Code 2 colors points by group

D Both codes color all points red

💡 Hint

aes() maps data variables to aesthetics; setting color outside aes() applies a fixed color.

In Code 1, color is mapped to the group variable, so points get different colors by group. In Code 2, color is fixed to red for all points.

🚀 Application

expert

Count of points plotted with filtering in geom_point

Given this code, how many points will be shown in the scatter plot?

R Programming

library(ggplot2)
data <- data.frame(x = 1:6, y = c(3, 5, 7, 9, 11, 13))
ggplot(data, aes(x = x, y = y)) + geom_point(data = subset(data, y > 7))

A 3 points

B 0 points

C 4 points

D 6 points

💡 Hint

Look at the subset condition y > 7 and count how many rows satisfy it.

Only points with y values greater than 7 are plotted. y values are 3,5,7,9,11,13 so points with y=9,11,13 qualify (3 points).