Knowledge Quiz

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You run ggplot(data = mpg) on its own and see a blank grey rectangle with no points, bars, or lines on it. Which of the following, if added, would fix this?

+ theme_bw()+ labs(title = "My Plot")+ geom_point(aes(x = displ, y = hwy))+ aes(x = displ, y = hwy, colour = class)

• Wrong: theme_bw() only changes background styling; it doesn’t add any visual marks.
• Wrong: labs() only changes text labels; it doesn’t add any visual marks.
• Correct: a geometry layer tells ggplot2 how to draw the mapped data, which is exactly what’s missing.
• Wrong: an aesthetic mapping only tells ggplot2 which variables to use and how; without a geom, there is still nothing telling it how to draw them. Meta-information

You run the following code:

ggplot(mpg, aes(x = displ, y = hwy)) +
geom_point() +
geom_smooth()

What best describes the resulting plot?

Both a scatterplot of the points and a smoothed trend line are drawn on top of each other.Only the trend line from geom_smooth() is drawn, because it overwrites the geom_point() layer.Only the points are drawn, because geom_smooth() needs its own aes() mapping to work.R throws an error, because a plot can only contain one geometry layer.

• Correct: each geom layer adds its own visual marks on top of the existing plot, so both the points and the smoothed line appear together.
• Wrong: adding a layer with + never removes an earlier layer; layers stack rather than replace one another.
• Wrong: geoms inherit the x/y mapping from ggplot() unless they specify their own, so geom_smooth() works here without an extra aes() call.
• Wrong: ggplot2 plots can combine as many geometry layers as needed in a single plot.

Which statements correctly describe labs() and theme_*() functions in ggplot2? (Select all that apply.)

labs() can rename axis titles, legend titles, and the plot title.Adding + theme_bw() to a saved plot object requires you to redefine the data and geometry layers from scratch.theme_minimal() and theme_classic() change the plot’s non-data styling (background, gridlines, etc.), not the data itself.theme_bw() changes which variables are mapped to x and y.

• TRUE: labs() accepts arguments matching any aesthetic or title role you want to relabel.
• FALSE: + layers are additive; a saved plot object already contains its data, mapping, and geometry, and a theme layer is simply appended on top.
• TRUE: this is exactly what a theme controls: appearance, not the underlying mappings or geometry.
• FALSE: themes never change what data is mapped to which aesthetic; that is controlled entirely by aes().