eda_3pt: 3-point summary plot

In mgimond/tukeyedar: Tukey Inspired Exploratory Data Analysis Functions

3-point summary plot

Description

eda_3pt splits the data into 3 groups (whose summary locations are defined by their respective medians), and two half slopes linking the groups. The function will return a scatter plot showing the half-slopes in red solid lines. The solid grey slope linking both tail-end groups shows the desired shape for both half-slopes. The goal is to have the two halve slopes line up as closely as possible to the solid grey slope via re-expression techniques when seeking a linear relationship between both variables.

The function will also return the half-slopes ratio hsrtio and the direction of re-expression for both X and Y values on the ladder of powers.

Usage

eda_3pt(
  dat,
  x,
  y,
  px = 1,
  py = 1,
  tukey = TRUE,
  axes = TRUE,
  pch = 21,
  equal = TRUE,
  p.col = "grey50",
  p.fill = "grey80",
  size = 0.8,
  alpha = 0.7,
  xlab = NULL,
  ylab = NULL,
  dir = TRUE,
  grey = 0.6,
  ...
)

Arguments

dat	Dataframe.
x	Variable assigned the x axis.
y	Variable assigned the y axis.
px	Power transformation to apply to the x-variable.
py	Power transformation to apply to the y-variable.
tukey	Boolean determining if a Tukey transformation should be adopted (FALSE adopts a Box-Cox transformation).
axes	Boolean determining if axes are to be drawn.
pch	Point symbol type.
equal	Boolean determining if axes lengths should match (i.e. square plot).
p.col	Color for point symbol.
p.fill	Point fill color passed to bg (Only used for pch ranging from 21-25).
size	Point size (0-1).
alpha	Point transparency (0 = transparent, 1 = opaque). Only applicable if rgb() is not used to define point colors.
xlab	X label for output plot.
ylab	Y label for output plot.
dir	Boolean indicating if suggested ladder of power direction should be displayed.
grey	Grey level to apply to plot elements (0 to 1 with 1 = black).
...	Other parameters passed to the graphics::plot function.

Details

Computes the three-point summary originally defined in Tukey's EDA book (see reference).

Value

Generates a plot and returns a list with the following named components:

• hsrtio: The ratio between both slopes. A value close to one suggests that no transformation is needed.

• xmed: The x-coordinate values for the three summary points.

• ymed: The y-coordinate values for the three summary points.

References

• Velleman, P. F., and D. C. Hoaglin. 1981. Applications, Basics and Computing of Exploratory Data Analysis. Boston: Duxbury Press.

• D. C. Hoaglin, F. Mosteller, and J. W. Tukey. 1983. Understanding Robust and Exploratory Data Analysis. Wiley.

• Tukey, John W. 1977. Exploratory Data Analysis. Addison-Wesley.

Examples

hsratio <- eda_3pt(cars, speed, dist)
hsratio <- eda_3pt(cars, speed, dist, py = 1/3, ylab=expression("Dist"^{1/3}))

#' # This next example models gas consumption as a function of engine displacement.
# It applies a transformation to both variables via the px and py arguments.
eda_3pt(mtcars, disp, mpg,  px = -1/3, py = -1,
       ylab = "gal/mi", xlab = expression("Displacement"^{-1/3}))

mgimond/tukeyedar documentation built on Feb. 1, 2025, 4:02 a.m.