R Programming Language Certification Data Visualization & Graphics in R 2

Question 1

Which ggplot2 geom creates a bar chart by counting occurrences of each category?

Accepted Answer

geom_bar()

Answer

geom_bar() automatically counts observations per category and plots those counts as bar heights.

Question 2

What argument in geom_bar() or geom_col() maps the fill color to a variable?

Accepted Answer

fill inside aes()

Answer

Mapping fill inside aes(), e.g. aes(fill = variable), assigns bar fill colors based on a data variable.

Question 3

Which function in ggplot2 adds a smooth trend line (e.g., loess or linear) to a plot?

Accepted Answer

geom_smooth()

Answer

geom_smooth() adds a smoothed conditional mean line with optional confidence interval shading.

Question 4

What does coord_flip() do in ggplot2?

Accepted Answer

Swaps the x and y axes

Answer

coord_flip() exchanges the x and y axes, which is useful for creating horizontal bar charts.

Question 5

Which R package extends ggplot2 to create interactive web-based plots?

Accepted Answer

plotly

Answer

plotly's ggplotly() function converts ggplot2 objects into interactive plotly visualizations with hover and zoom.

R Programming Language Certification Practice Test