Bar plots (geom_bar, geom_col) in R Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main difference between geom_bar() and geom_col() in ggplot2?

geom_bar() counts the number of cases at each x value and plots the height automatically.

geom_col() uses the y values you provide directly to set the height of the bars.

beginner

How does geom_bar() behave if you provide a y aesthetic?

geom_bar() ignores the y aesthetic because it is designed to count observations. To plot heights from y values, use geom_col().

beginner

Write a simple example of geom_bar() to plot counts of a categorical variable category in a data frame df.

ggplot(df, aes(x = category)) + geom_bar()

This will count how many times each category appears and draw bars accordingly.

beginner

Write a simple example of geom_col() to plot values from a data frame df with columns category and value.

ggplot(df, aes(x = category, y = value)) + geom_col()

This will draw bars with heights equal to the value for each category.

beginner

Why might you choose geom_col() over geom_bar()?

Use geom_col() when you already have summarized data with values you want to plot as bar heights. geom_bar() is for raw data where you want to count occurrences.

Which function automatically counts the number of observations for each x value in ggplot2?

A geom_bar()

B geom_col()

C geom_point()

D geom_line()

geom_bar() counts observations and plots bar heights accordingly.

If you have a data frame with categories and their sales numbers, which geom should you use to plot sales as bar heights?

A geom_bar()

B geom_col()

C geom_histogram()

D geom_boxplot()

geom_col() uses the y values you provide, perfect for plotting sales numbers.

What happens if you provide a y aesthetic to geom_bar()?

A It uses y to set bar heights

B It plots a line instead

C It ignores y and counts observations

D It throws an error

geom_bar() ignores y because it is designed to count data, not use y values.

Which ggplot2 function would you use to plot the frequency of a categorical variable?

A geom_text()

B geom_col()

C geom_point()

D geom_bar()

geom_bar() is used to plot counts or frequencies of categories.

You want to plot a bar chart from summarized data with values already calculated. Which is best?

A geom_col()

B geom_histogram()

C geom_bar()

D geom_area()

geom_col() plots bars using the provided y values, ideal for summarized data.

Explain the difference between geom_bar() and geom_col() and when to use each.

Think about whether you have raw data or summarized values.

Describe how you would create a bar plot showing the number of items in each category using ggplot2.

Counting categories is automatic with geom_bar.