latticeExtra (version 0.6-9)

panel.lmlineq: Draw a line with a label, by default its equation

Description

This is an extension of the panel functions panel.abline and panel.lmline to also draw a label on the line. The default label is the line equation, and optionally the R squared value of its fit to the data points.

Usage

panel.ablineq(a = NULL, b = 0,
              h = NULL, v = NULL,
              reg = NULL, coef = NULL,
              pos = if (rotate) 1 else NULL,
              offset = 0.5, adj = NULL,
              at = 0.5, x, y,
              rotate = FALSE, srt = 0,
              label = NULL,
              varNames = alist(y = y, x = x),
              varStyle = "italic",
              fontfamily = "serif",
              digits = 3,
              r.squared = FALSE, sep = ", ", sep.end = "",
              col, col.text, col.line,
              ..., reference = FALSE)

panel.lmlineq(x, y, ...)

Arguments

a, b, h, v, reg, coef

specification of the line. The simplest usage is to give a and b to describe the line y = a + b x. Horizontal or vertical lines can be specified as arguments h or v, respecti

pos, offset, adj, fontfamily

passed on to panel.text. For pos: 1 = below, 2 = left, 3 = above, 4 = right, and the offset (in character widths) is applied. For adj: c(0,0) = a

at

position of the equation as a fractional distance along the line. This should be in the range 0 to 1. When a vertical line is drawn, this gives the vertical position of the equation.

x, y

position of the equation in native units. If given, this over-rides at. For panel.lmlineq this is the data, passed on as lm(y ~ x).

rotate, srt

set rotate = TRUE to align the equation with the line. This will over-ride srt, which otherwise gives the rotation angle. Note that the calculated angle depends on the current device size; this will be wrong i

label

the text to draw along with the line. If specified, this will be used instead of an equation.

varNames

names to display for x and/or y. This should be a list like list(y = "Q", x = "X") or, for mathematical symbols, alist(y = (alpha + beta), x = sqrt(x[t])).

varStyle

the name of a plotmath function to wrap around the equation expression, or NULL. E.g. "bolditalic", "displaystyle".

digits

number of decimal places to show for coefficients in equation.

r.squared, sep, sep.end

the $R^2$ statistic to display along with the equation of a line. This can be given directly as a number, or TRUE, in which case the function expects a model object (typically lm) and

..., col, col.text, col.line

passed on to panel.abline and panel.text. Note that col applies to both text and line; col.text applies to t

reference

whether to draw the line in a "reference line" style, like that used for grid lines.

Details

The equation is constructed as an expression using plotmath.

See Also

panel.abline, panel.text, lm, plotmath

Examples

set.seed(0)
xsim <- rnorm(50, mean = 3)
ysim <- (0 + 2 * xsim) * (1 + rnorm(50, sd = 0.3))

## basic use as a panel function
xyplot(ysim ~ xsim, panel = function(x, y, ...) {
  panel.xyplot(x, y, ...)
  panel.ablineq(a = 0, b = 2, adj = c(0,1))
  panel.lmlineq(x, y, adj = c(1,0), lty = 2,
                col.line = "grey", digits = 1)
})

## using layers:
xyplot(ysim^2 ~ xsim) +
  layer(panel.ablineq(lm(y ~ x, subset = x <= 3),
    varNames = alist(y = y^2, x = x[x <= 3]), pos = 4))

## rotated equation (depends on device aspect at plotting time)
xyplot(ysim ~ xsim) +
  layer(panel.ablineq(lm(y ~ x), rotate = TRUE, at = 0.8))

## horizontal and vertical lines
xyplot(ysim ~ xsim) +
  layer(panel.ablineq(v = 3, pos = 4, at = 0.1, lty = 2,
                      label = "3.0 (critical value)")) +
  layer(panel.ablineq(h = mean(ysim), pos = 3, at = 0.15, lty = 2,
                      varNames = alist(y = plain(mean)(y))))

## using layer styles, r.squared
xyplot(ysim ~ xsim) +
  layer(panel.ablineq(lm(y ~ x), r.sq = TRUE,
                      at = 0.4, adj=0:1), style = 1) +
  layer(panel.ablineq(lm(y ~ x + 0), r.sq = TRUE,
                      at = 0.6, adj=0:1), style = 2)

## alternative placement of equations
xyplot(ysim ~ xsim) +
  layer(panel.ablineq(lm(y ~ x), r.sq = TRUE, rot = TRUE,
                      at = 0.8, pos = 3), style = 1) +
  layer(panel.ablineq(lm(y ~ x + 0), r.sq = TRUE, rot = TRUE,
                      at = 0.8, pos = 1), style = 2)

update(trellis.last.object(),
  auto.key = list(text = c("intercept", "no intercept"),
                  points = FALSE, lines = TRUE))