Plot of Domain and Median Differences of Two "hexbin" Objects

Let bin1 and bin2 represent two hexbin objects with scaling, plot shapes, and bin sizes. This plot distinguishes cells unique to bin1, cells in common, and cells unique to bin2 using color. When the erode components are present, color also distinguishes the two erosion medians. An arrow shows the vector from the median of bin1 to the median of bin2.

hdiffplot(bin1, bin2 = NULL, xbnds, ybnds,
          focus = NULL,<!-- % if(is.null(bin2)) 1:length(bin1) else c(1, 2), -->
          col.control = list(medhex = "white", med.bord = "black",
          focus = NULL, focus.border = NULL, back.col = "grey"),
          arrows = TRUE, size = unit(0.1, "inches"), lwd = 2,
          eps = 1e-6, unzoom = 1.08, clip="off", xlab = "", ylab = "",
          main = deparse(mycall), ...)

Arguments

bin1, bin2

two objects of class hexbin.

xbnds,ybnds

global x- and y-axis plotting limits. Used primarily for multiple comparison plots.

focus

a vector of integers specifying which hexbin objects should be treated as focal. Excluded hexbins are treated as background.

col.control

a list for detailed color control.

arrows

a logical indicating wheter or not to draw arrows between the focal hexbin objects median cells.

border

border arguments to polygon

size

arrow type size in inches.

eps

distance criteria for distinct medians

unzoom

plot limit expansion factor when xbnds is missing

clip

either 'on' or 'off' are the allowed arguments, when on everything is clipped to the plotting region.

lwd

Line width for arrows, ignored when arrows=FALSE or when bins have no erosion component

xlab

label for x-axis

ylab

label for y-axis

main

main title for the plot; automatically constructed by default.

...

...............

Details

The hexbin objects for comparison, bin1 and bin2, must have the same plotting limits and cell size. The plot produces a comparison overlay of the cells in the two objects. If external global scaling is not supplied, the algorithm determines plotting limits to increase resolution. For example, the objects may be the result of the erode.hexbin() and include only high count cells containing 50 of the counts. The density, border, and pen arguments correspond to the polygon function calls for plotting six types of cells. The cell types are respectively:

unique cells of bin1,
joint cells,
unique cells of bin2,
median cell of bin1,
median cell of bin2,
median cell if identical.

The erode components of the hexbin objects must be present for the medians to plot. The algorithm select a single cell for the median if there are algorithmic ties.

The pen numbers for types of cells start at Pen 2. Pen 1 is presumed black. The suggested six additional colors are light blue, light gray, light red, blue, red, and black. Carr (1991) shows an example for black and white printing. That plot changes the six colors to light gray, dark gray, white, black, black, and black. It changes the 4th, 5th, and 6th argument of border to TRUE. It also changes 4th, 5th and 6th argument of density to 0. In other words cells in common do not show and medians cells appear as outlines.

When xbnds is missing, the plot changes graphics parameters and resets them. The function also zooms in based on the available data to provide increased resolution.

References

see in grid.hexagons.

Examples

## Comparison of two bivariate boxplots
x1 <- rnorm(10000)
y1 <- rnorm(10000)
x2 <- rnorm(10000,mean=.5)
y2 <- rnorm(10000,mean=.5)
xbnds <- range(x1,x2)
ybnds <- range(y1,y2)

bin1 <- hexbin(x1,y1,xbnds=xbnds,ybnds=ybnds)
bin2 <- hexbin(x2,y2,xbnds=xbnds,ybnds=ybnds)
erodebin1 <- erode.hexbin(smooth.hexbin(bin1))
erodebin2 <- erode.hexbin(smooth.hexbin(bin2))

hdiffplot(erodebin1,erodebin2)


## Compare  *three* of them: --------------------

x3 <- rnorm(10000,mean=-1)
y3 <- rnorm(10000,mean=-.5)
xbnds <- range(x1,x2,x3)
ybnds <- range(y1,y2,y3)

bin1 <- hexbin(x1,y1,xbnds=xbnds,ybnds=ybnds)
bin2 <- hexbin(x2,y2,xbnds=xbnds,ybnds=ybnds)
bin3 <- hexbin(x3,y3,xbnds=xbnds,ybnds=ybnds)
erodebin1 <- erode.hexbin(smooth.hexbin(bin1))
erodebin2 <- erode.hexbin(smooth.hexbin(bin2))
erodebin3 <- erode.hexbin(smooth.hexbin(bin3))

bnlst <- list(b1=erodebin1, b2=erodebin2, b3=erodebin3)
hdiffplot(bnlst)