pairs {graphics}R Documentation

Scatterplot Matrices

Description

A matrix of scatterplots is produced.

Usage

pairs(x, ...)

## S3 method for class 'formula':
pairs(formula, data = NULL, ..., subset)

## Default S3 method:
pairs(x, labels, panel = points, ...,
      lower.panel = panel, upper.panel = panel,
      diag.panel = NULL, text.panel = textPanel,
      label.pos = 0.5 + has.diag/3,
      cex.labels = NULL, font.labels = 1,
      row1attop = TRUE, gap = 1)

Arguments

x the coordinates of points given as columns of a matrix.
formula a formula, such as ~ x + y + z. Each term will give a separate variable in the pairs plot, so terms should be numeric vectors. (A response will be interpreted as another variable, but not treated specially, so it is confusing to use one.)
data a data.frame (or list) from which the variables in formula should be taken.
subset an optional vector specifying a subset of observations to be used for plotting.
labels the names of the variables.
panel function(x,y,...) which is used to plot the contents of each panel of the display.
... graphical parameters can be given as arguments to plot.
lower.panel, upper.panel separate panel functions to be used below and above the diagonal respectively.
diag.panel optional function(x, ...) to be applied on the diagonals.
text.panel optional function(x, y, labels, cex, font, ...) to be applied on the diagonals.
label.pos y position of labels in the text panel.
cex.labels, font.labels graphics parameters for the text panel.
row1attop logical. Should the layout be matrix-like with row 1 at the top, or graph-like with row 1 at the bottom?
gap Distance between subplots, in margin lines.

Details

The ijth scatterplot contains x[,i] plotted against x[,j]. The “scatterplot” can be customised by setting panel functions to appear as something completely different. The off-diagonal panel functions are passed the appropriate columns of x as x and y: the diagonal panel function (if any) is passed a single column, and the text.panel function is passed a single (x, y) location and the column name.

The graphical parameters pch and col can be used to specify a vector of plotting symbols and colors to be used in the plots.

The graphical parameter oma will be set by pairs.default unless supplied as an argument.

A panel function should not attempt to start a new plot, but just plot within a given coordinate system: thus plot and boxplot are not panel functions.

For the default method, missing values are passed to the panel functions and will often be ignored within a panel. However, for the formula method and the default value of na.action, all cases which contain a missing values for any of the variables are omitted completely (including when the scales are selected). [The behaviour of the formula method will be changed in R 2.0.0.]

Author(s)

Enhancements for R 1.0.0 contributed by Dr. Jens Oehlschlaegel-Akiyoshi and R-core members.

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

Examples

data(iris)
pairs(iris[1:4], main = "Anderson's Iris Data -- 3 species",
      pch = 21, bg = c("red", "green3", "blue")[unclass(iris$Species)])

## formula method
data(swiss)
pairs(~ Fertility + Education + Catholic, data = swiss,
      subset = Education < 20, main = "Swiss data, Education < 20")

data(USJudgeRatings)
pairs(USJudgeRatings)

## put histograms on the diagonal
panel.hist <- function(x, ...)
{
    usr <- par("usr"); on.exit(par(usr))
    par(usr = c(usr[1:2], 0, 1.5) )
    h <- hist(x, plot = FALSE)
    breaks <- h$breaks; nB <- length(breaks)
    y <- h$counts; y <- y/max(y)
    rect(breaks[-nB], 0, breaks[-1], y, col="cyan", ...)
}
pairs(USJudgeRatings[1:5], panel=panel.smooth,
      cex = 1.5, pch = 24, bg="light blue",
      diag.panel=panel.hist, cex.labels = 2, font.labels=2)

## put (absolute) correlations on the upper panels,
## with size proportional to the correlations.
panel.cor <- function(x, y, digits=2, prefix="", cex.cor)
{
    usr <- par("usr"); on.exit(par(usr))
    par(usr = c(0, 1, 0, 1))
    r <- abs(cor(x, y))
    txt <- format(c(r, 0.123456789), digits=digits)[1]
    txt <- paste(prefix, txt, sep="")
    if(missing(cex.cor)) cex <- 0.8/strwidth(txt)
    text(0.5, 0.5, txt, cex = cex * r)
}
pairs(USJudgeRatings, lower.panel=panel.smooth, upper.panel=panel.cor)
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