Week 2 Quiz:Exploratory Data Analysis(Data Science Specialization):Answers2025

Question 1

Under the lattice graphics system, what do the primary plotting functions like xyplot() and bwplot() return?

✅ an object of class “trellis”
❌ nothing; only a plot is made
❌ an object of class “lattice”
❌ an object of class “plot”

Explanation:
Lattice plotting functions return an object of class “trellis”, which represents the entire plot and can be printed or modified later.

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Question 2

What is produced by the following code?

✅ A set of 3 panels showing the relationship between weight and time for each diet.
❌ A set of 11 panels showing the relationship between weight and diet for each time.
❌ A set of 16 panels showing the relationship between weight and time for each rat.
❌ A set of 3 panels showing the relationship between weight and time for each rat.

Explanation:
Diet has 3 factor levels, so conditioning by Diet (| Diet) creates 3 panels, one for each diet, showing weight vs Time.

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Question 3

Which of the following functions can be used to annotate the panels in a multi-panel lattice plot?

✅ panel.abline()
❌ text()
❌ lines()
❌ points()
❌ axis()

Explanation:
In lattice, annotation within panels is handled by panel functions such as panel.abline(), panel.points(), etc., not base graphics functions.

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Question 4

The following code does NOT result in a plot appearing:

✅ The object ‘p’ has not yet been printed with the appropriate print method.
❌ There is a syntax error in xyplot()
❌ Variables not found in dataset
❌ xyplot() sends plots to PDF by default

Explanation:
Lattice plots only appear when printed. In an interactive session, xyplot() prints automatically, but if assigned to a variable (p), you must explicitly call print(p).

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Question 5

In the lattice system, which function controls the appearance of all lattice plots?

✅ trellis.par.set()
❌ splom()
❌ print.trellis()
❌ par()

Explanation:
trellis.par.set() adjusts global graphical parameters (colors, line types, fonts) for lattice plots, similar to par() in base graphics.

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Question 6

What is ggplot2 an implementation of?

✅ the Grammar of Graphics developed by Leland Wilkinson
❌ a 3D visualization system
❌ the S language from Bell Labs
❌ the base plotting system in R

Explanation:
ggplot2 implements the Grammar of Graphics, providing a structured way to build plots layer by layer.

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Question 7

To visualize how ozone vs wind varies by month using ggplot2:

✅

❌ qplot(Wind, Ozone, data = airquality, facets = . ~ factor(Month))
❌ qplot(Wind, Ozone, data = airquality, geom = "smooth")
❌ qplot(Wind, Ozone, data = airquality)

Explanation:
Converting Month to a factor ensures proper paneling across months using facets = . ~ Month.

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Question 8

What is a geom in ggplot2?

✅ a plotting object like point, line, or other shape
❌ a method for mapping data to color/size
❌ a statistical transformation
❌ a method for conditioning plots

Explanation:
A geom defines the type of plot layer, e.g., geom_point(), geom_line(), etc.

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Question 9

Why does this code fail to produce a plot?

✅ ggplot does not yet know what type of layer to add to the plot.
❌ The dataset is too large
❌ Syntax error
❌ Object ‘g’ has no print method

Explanation:
ggplot() only defines the aesthetic mappings. You must add a layer (like + geom_point()) to specify what to draw.

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Question 10

Add a smoother to a ggplot2 scatterplot:

✅ qplot(votes, rating, data = movies) + geom_smooth()
❌ qplot(votes, rating, data = movies) + stats_smooth("loess")
❌ qplot(votes, rating, data = movies, panel = panel.loess)
❌ qplot(votes, rating, data = movies, smooth = "loess")

Explanation:
In ggplot2, layers are added with +. geom_smooth() adds a smoothing curve (LOESS or linear).

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🧾 Summary Table

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