panel.functions Useful Panel Function Components

Description

These are predefined panel functions available in lattice for use in constructing new panel functions (often on-the-fly).

Usage

panel.abline(a = NULL, b = 0,
             h = NULL, v = NULL,
             reg = NULL, coef = NULL,
             col, col.line, lty, lwd, alpha, type,
             ...,
             reference = FALSE,
             identifier = "abline")
panel.refline(...) 

panel.curve(expr, from, to, n = 101,
            curve.type = "l",
            col, lty, lwd, type,
            ...,
            identifier = "curve")
panel.rug(x = NULL, y = NULL,
          regular = TRUE, 
          start = if (regular) 0 else 0.97,
          end = if (regular) 0.03 else 1,
          x.units = rep("npc", 2),
          y.units = rep("npc", 2),
          col, col.line, lty, lwd, alpha,
          ...,
          identifier = "rug")
panel.average(x, y, fun = mean, horizontal = TRUE,
              lwd, lty, col, col.line, type,
              ...,
              identifier = "linejoin")
panel.linejoin(x, y, fun = mean, horizontal = TRUE,
               lwd, lty, col, col.line, type,
               ...,
               identifier = "linejoin")





panel.fill(col, border, ..., identifier = "fill")
panel.grid(h=3, v=3, col, col.line, lty, lwd, x, y, ..., identifier = "grid")
panel.lmline(x, y, ..., identifier = "lmline")
panel.mathdensity(dmath = dnorm, args = list(mean=0, sd=1),
                  n = 50, col, col.line, lwd, lty, type,
                  ..., identifier = "mathdensity")

Arguments

x, y	Variables defining the contents of the panel. In panel.grid these are optional and are used only to choose an appropriate method of pretty.
a, b	Coefficients of the line to be added by panel.abline. a can be a vector of length 2, representing the coefficients of the line to be added, in which case b should be missing. a can also be an appropriate ‘regression’ object, i.e., an object which has a coef method that returns a length 2 numeric vector. The corresponding line will be plotted. The reg argument overrides a if specified.
coef	Coefficients of the line to be added as a vector of length 2.
reg	A (linear) regression object, with a coef method that gives the coefficints of the corresponding regression line.
h, v	For panel.abline, these are numeric vectors giving locations respectively of horizontal and vertical lines to be added to the plot, in native coordinates. For panel.grid, these usually specify the number of horizontal and vertical reference lines to be added to the plot. Alternatively, they can be negative numbers. h=-1 and v=-1 are intended to make the grids aligned with the axis labels. This doesn't always work; all that actually happens is that the locations are chosen using pretty, which is also how the label positions are chosen in the most common cases (but not for factor variables, for instance). h and v can be negative numbers other than -1, in which case -h and -v (as appropriate) is supplied as the n argument to pretty. If x and/or y are specified in panel.grid, they will be used to select an appropriate method for pretty. This is particularly useful while plotting date-time objects.
reference	A logical flag determining whether the default graphical parameters for panel.abline should be taken from the “reference.line” parameter settings. The default is to take them from the “add.line” settings. The panel.refline function is a wrapper around panel.abline that calls it with reference = TRUE.
expr	An expression considered as a function of x, or a function, to be plotted as a curve.
n	The number of points to use for drawing the curve.
from, to	optional lower and upper x-limits of curve. If missing, limits of current panel are used
curve.type	Type of curve ("p" for points, etc), passed to llines
regular	A logical flag indicating whether the ‘rug’ is to be drawn on the ‘regular’ side (left / bottom) or not (right / top).
start, end	endpoints of rug segments, in normalized parent coordinates (between 0 and 1). Defaults depend on value of regular, and cover 3% of the panel width and height.
x.units, y.units	Character vectors, replicated to be of length two. Specifies the (grid) units associated with start and end above. x.units and y.units are for the rug on the x-axis and y-axis respectively (and thus are associated with start and end values on the y and x scales respectively).
col, col.line, lty, lwd, alpha, border	Graphical parameters.
type	Usually ignored by the panel functions documented here; the argument is present only to make sure an explicitly specified type argument (perhaps meant for another function) does not affect the display.
fun	The function that will be applied to the subset of x values (or y if horizontal is FALSE) determined by the unique values of y (x).
horizontal	A logical flag. If FALSE, the plot is ‘transposed’ in the sense that the roles of x and y are switched; x is now the ‘factor’. Interpretation of other arguments change accordingly. See documentation of bwplot for a fuller explanation.
dmath	A vectorized function that produces density values given a numeric vector named x, e.g., dnorm.
args	A list giving additional arguments to be passed to dmath.
...	Further arguments, typically graphical parameters, passed on to other low-level functions as appropriate. Color can usually be specified by col, col.line, and col.symbol, the last two overriding the first for lines and points respectively.
identifier	A character string that is prepended to the names of grobs that are created by this panel function.

Details

panel.abline adds a line of the form y = a + b * x, or vertical and/or horizontal lines. Graphical parameters are obtained from the “add.line” settings by default. panel.refline is similar, but uses the “reference.line” settings for the defaults.

panel.grid draws a reference grid.

panel.curve adds a curve, similar to what curve does with add = TRUE. Graphical parameters for the curve are obtained from the “add.line” setting.

panel.average treats one of x and y as a factor (according to the value of horizontal), calculates fun applied to the subsets of the other variable determined by each unique value of the factor, and joins them by a line. Can be used in conjunction with panel.xyplot, and more commonly with panel.superpose to produce interaction plots.

panel.linejoin is an alias for panel.average. It is retained for back-compatibility, and may go away in future.

panel.mathdensity plots a (usually theoretical) probability density function. This can be useful in conjunction with histogram and densityplot to visually assess goodness of fit (note, however, that qqmath is more suitable for this).

panel.rug adds a rug representation of the (marginal) data to the panel, much like rug.

panel.lmline(x, y) is equivalent to panel.abline(lm(y ~ x)).

Author(s)

Deepayan Sarkar [email protected]

See Also

Lattice, panel.axis, panel.identify identify, trellis.par.set.

Examples

## Interaction Plot

bwplot(yield ~ site, barley, groups = year,
       panel = function(x, y, groups, subscripts, ...) {
           panel.grid(h = -1, v = 0)
           panel.stripplot(x, y, ..., jitter.data = TRUE,
                           groups = groups, subscripts = subscripts)
           panel.superpose(x, y, ..., panel.groups = panel.average,
                           groups = groups, subscripts = subscripts)
       },
       auto.key =
       list(points = FALSE, lines = TRUE, columns = 2))

## Superposing a fitted normal density on a Histogram

histogram( ~ height | voice.part, data = singer, layout = c(2, 4),
          type = "density", border = "transparent", col.line = "grey60",
          xlab = "Height (inches)",
          ylab = "Density Histogram\n with Normal Fit",
          panel = function(x, ...) {
              panel.histogram(x, ...)
              panel.mathdensity(dmath = dnorm,
                                args = list(mean=mean(x),sd=sd(x)), ...)
          } )