Draw two plot series with different y scales

Overplot two trellis objects with different y scales, optionally in different styles, adding a second y axis, and/or a second y axis label.

Note: drawing plots with multiple scales is often a bad idea as it can be misleading.

doubleYScale(obj1, obj2, use.style = TRUE,
             style1 = if (use.style) 1, style2 = if (use.style) 2,
             add.axis = TRUE, add.ylab2 = FALSE,
             text = NULL, auto.key = if (!is.null(text))
               list(text, points = points, lines = lines, ...),
             points = FALSE, lines = TRUE, ..., under = FALSE)

Arguments

obj1, obj2

trellis objects. Note that most settings, like main/sub/legend/etc are taken only from obj1; only the panel, axis and ylab are taken from obj2.

use.style, style1, style2

style1 and style2 give the `group number' for obj1 and obj2 respectively. The style is taken from these indices into the values of trellis.par.get("superpose.line"). Therefore these should be integers between 1 and 6; a value of 0 or NULL can be given to leave the default settings. These will also be applied to the y-axes and ylab, if relevant. use.style simply changes the defaults of the style arguments.

add.axis

if TRUE, draw a second y axis (for the obj2 series) on the right side of the plot.

add.ylab2

if TRUE, draw a second y axis label (from obj2$ylab) on the right side of the plot. Note, this will replace any existing key or legend on the right side, i.e. with space = "right".

text, auto.key, points, lines, ...

if non-NULL, add a key to the display, using entries named by text. Further arguments are passed on to simpleKey at plot time.

under

if TRUE, draw obj2 under obj1.

Details

Panels from the trellis object obj2 will be drawn in the corresponding panel of obj1.

Axis settings are taken from the trellis objects, so most scales arguments such as draw, at, labels etc from obj2 will carry over to the second y axis.

Value

a merged trellis object.

Author

Felix Andrews felix@nfrac.org

See also

as.layer

Examples

set.seed(1)
foo <- list(x = 1:100, y = cumsum(rnorm(100)))
## show original data
xyplot(y + y^2 ~ x, foo, type = "l")

## construct separate plots for each series
obj1 <- xyplot(y ~ x, foo, type = "l")
obj2 <- xyplot(y^2 ~ x, foo, type = "l")
## simple case: no axis for the overlaid plot
doubleYScale(obj1, obj2, add.axis = FALSE)

## draw second y axis
doubleYScale(obj1, obj2)

## ...with second ylab
doubleYScale(obj1, obj2, add.ylab2 = TRUE)

## ...or with a key
doubleYScale(obj1, obj2, text = c("obj1", "obj2"))

## ...with custom styles
update(doubleYScale(obj1, obj2, text = c("obj1", "obj2")),
  par.settings = simpleTheme(col = c('red','black'), lty = 1:2))


## different plot types
x <- rnorm(60)
doubleYScale(histogram(x), densityplot(x), use.style = FALSE)

## (but see ?as.layer for a better way to do this)

## multi-panel example
## a variant of Figure 5.13 from Sarkar (2008)
## http://lmdvr.r-forge.r-project.org/figures/figures.html?chapter=05;figure=05_13
data(SeatacWeather)
temp <- xyplot(min.temp + max.temp ~ day | month,
               data = SeatacWeather, type = "l", layout = c(3, 1))
rain <- xyplot(precip ~ day | month, data = SeatacWeather, type = "h")

doubleYScale(temp, rain, style1 = 0, style2 = 3, add.ylab2 = TRUE,
   text = c("min. T", "max. T", "rain"), columns = 3)


## re-plot with different styles
update(trellis.last.object(),
   par.settings = simpleTheme(col = c("black", "red", "blue")))