Graphics

Question 1

plot()

Answer 1

• Function in base R t hat is the most important high level function.
• First argument is data, usually a vector, but could be a data frame.
• Second argument can also be data, but could also be almost anything.

Question 2

plot() a data frame

Answer 2

• plot(data) gives a scatterplot matrix.

Question 3

plot() two vectors

Answer 3

• plot(x_variable or x_dataframe_column, y_variable or y_dataframe_column).
• Implies “y as a function of x”.

Question 4

par(mfrow=c())

Answer 4

• Function nested that will essentially create spaces in an imaginary matrix in which to fill in with plots and graphs.
• Determines how many graphics will appear in a single plot window.

Question 5

par()

Answer 5

• Function to examine the default graphical settings.

Question 6

Colors

Answer 6

• 657 base colors in R.
  1) col=
  2) fg =
  3) bg =
  4) col.main =
  5) col.axis =
• When putting colors in the arugments using the c() function, must have parantheses, be all lower case, and be surrounded by quotations.

Question 7

col =

Answer 7

• Option used for the colors of lines, symbols and text.

Question 8

fg =

Answer 8

• Option used for colors of axes and borders.

Question 9

bg =

Answer 9

• Option used for the color of the background or fill.

Question 10

col.main =

Answer 10

• Option used for the color for the plot title.

Question 11

col.axis =

Answer 11

• Option used for the color for the axis labels.

Question 12

lty =

Answer 12

• Option that controls the appearance of lines on a plot.

- Values 1 - 6 are used to create different line styles.

Question 13

lwd =

Answer 13

• Option that controls the line thickness.

- Defaults to 1 + lwd = 2 is twice as thick as default, lwd = 3 is three times as thick, etc.

Question 14

ps =

Answer 14

• Option that controls the absolute font size setting.

- Default is 16.

Question 15

cex =

Answer 15

• Option that controls character expansion = size of the text.
• Multiplier and default is 1.
• Final font specification is ps * cex.
• Can also affect plot symbols.

Question 16

cex.axis =

Answer 16

• Option that controls the text draw as tick labels.

Question 17

cex.lab =

Answer 17

• Option that controls the text of the axis labels.

Question 18

cex.main =

Answer 18

• Option that controls the text of the title.

Question 19

cex.sub =

Answer 19

• Option that controls the text of the subtitle.

Question 20

pch =

Answer 20

• Option that changes the plot symbol.

- Values are between 0 and 25.

Question 21

Barplot

Answer 21

• Displays the frequency or relative frequency for all observations of a categorical variable.
• Can be displayed horizontally or vertically.
• Can be grouped or stacked.

Question 22

Barplot Syntax

Answer 22

• barplot(height, width = 1, space = NULL, names.arg = NULL, legend.text = NULL, beside = FALSE, horiz = FALSE, density = NULL, angle = 45, col = NULL, border = par(“fg”), main = NULL, sub = NULL, xlab = NULL, ylab = NULL, xlim = NULL, ylim = NULL, xpd = TRUE, log = “”, axes = TRUE, axisnames = TRUE, cex.axis = par(“cex.axis”), cex.names = par(“cex.axis”),
  inside = TRUE, plot = TRUE, axis.lty = 0, offset = 0, add = FALSE, args.legend = NULL, …)

Question 23

names.arg =

Answer 23

• Option that allows us to change the default names.

Question 24

Histograms

Answer 24

• Total area under the histogram totals to 1.0 and is directly comparable to the estimates of its probability density function.
• Can create using the hist() function.

Question 25

truehist()

Answer 25

• Function in package MASS that produces a more accurate histogram than hist().

Question 26

hist() syntax

Answer 26

• Example: hist(rivers, main = “hist(rivers)”, freq = FALSE, col = “cyan”, xlab = “miles”).

Question 27

Mosaicplot

Answer 27

• A graphical representation of the two-way frequency table of Contingency Table.

Question 28

cor()

Answer 28

• Function that generate a correlation matrix from a data frame.

Question 29

pair()

Answer 29

• Function that creates a scatterplot matrix.

- Can be used on a matrix or data frame.

Question 30

boxplot()

Answer 30

• Function that is used to depict groupings of numerical data through their five-number summaries.
• Will indicate which observations might be considered outliers.
• Can draw horizontally or vertically.
• Can operate on a single vector of values but usually two or more vectors make better use of the data.

Question 31

Mapping in R

Answer 31

• Utilizes packages maps and mapdata.

Question 32

ggplot()

Answer 32

• Function that is used to initialize the basic graph structure which layers can then be added to.
• Easier to make complicated graphics, difficult to make simple graphics.

Question 33

ggplot() syntax

Answer 33

- ggplot(data = ,
aes(x = ,
y = ,
... ),
... ) +
- ggplot uses a "+" to separate layers.

Question 34

aes

Answer 34

• A feature of ggplot that is something you can see.
• Includes position (on the x and y axes), color (“outside” color), fill (“inside” color), shape (of points), linetype and size.

Question 35

Geoms

Answer 35

• A feature of ggplot that is used to describe the type of plot you want to produce.

Question 36

Scaling

Answer 36

• Part of ggplot2 = tells ggplot what aesthetics to use when mapping.

Question 37

Faceting (Grids)

Answer 37

• Subsetting in ggplot2.

- Create separate graphs for subsets of data.

Question 38

facet_wrap()

Answer 38

• Function in ggplot2 that defines subsets as the levels of a single grouping variable.

Question 39

facet_grid()

Answer 39

• Function in ggplot2 that defines subsets as the crossing of two grouping variables.

Question 40

Building a ggplot

Answer 40

• Need at least a base with the ggplot() function, a data from and a geom layer.