A function to compute false colors representing a numeric or categorical variable

Calculates false colors from a numeric variable (including factors, using their numeric codes) given a color scheme and breakpoints.

Usage

level.colors(x, at, col.regions, colors = TRUE, ...)

Arguments

x: A numeric or factor variable.
at: A numeric variable of breakpoints defining intervals along the range of x.
col.regions: A specification of the colors to be assigned to each interval defined by at. This could be either a vector of colors, or a function that produces a vector of colors when called with a single argument giving the number of colors. See details below.
colors: logical indicating whether colors should be computed and returned. If FALSE, only the indices representing which interval (among those defined by at) each value in x falls into is returned.
...: Extra arguments, ignored.

Value

A vector of the same length as x. Depending on the colors argument, this could be either a vector of colors (in a form usable by R), or a vector of integer indices representing which interval the values of x fall in.

Author

Deepayan Sarkar deepayan.sarkar@r-project.org

Details

If at has length n, then it defines n-1 intervals. Values of x outside the range of at are not assigned to an interval, and the return value is NA for such values.

Colors are chosen by assigning a color to each of the n-1 intervals. If col.regions is a palette function (such as topo.colors, or the result of calling colorRampPalette), it is called with n-1 as an argument to obtain the colors. Otherwise, if there are exactly n-1 colors in col.regions, these get assigned to the intervals. If there are fewer than n-1 colors, col.regions gets recycled. If there are more, a more or less equally spaced (along the length of col.regions) subset is chosen.

Examples


depth.col <-
    with(quakes, 
         level.colors(depth, at = do.breaks(range(depth), 30),
                      col.regions = hcl.colors))


xyplot(lat ~ long | equal.count(stations), quakes,
       strip = strip.custom(var.name = "Stations"),
       colours = depth.col,
       panel = function(x, y, colours, subscripts, ...) {
           panel.xyplot(x, y, pch = 21, col = "transparent",
                        fill = colours[subscripts], ...)
       })