Produce a legend for continuous gradient scales

Prints an annotated vertical bar coloured according to a continuous palette.

SpectrumLegend(
  x = "topright",
  ...,
  palette,
  legend,
  lty = 1,
  lwd = 4,
  bty = "o",
  adj = if (horiz) c(0.5, 0.5) else c(0, 0.5),
  horiz = FALSE,
  lend = "butt",
  cex = 1,
  seg.len = 1
)

SizeLegend(
  x = "topright",
  ...,
  legend = character(0),
  width = c(0, 1),
  palette = par("col"),
  scale = c("pch", "lwd"),
  lty = 0,
  lwd = 4,
  bty = "o",
  adj = if (horiz) c(0.5, 0.5) else c(0, 0.5),
  horiz = FALSE,
  lend = "butt",
  cex = 1,
  seg.len
)

Arguments

x, horiz, adj, seg.len, ...

Additional parameters to legend().

palette

Colour palette to depict. Specify either a vector of colours, or a function such that palette(n) returns a vector of n colours.

legend

Character vector with which to label points on palette. Note that, in a vertical legend, values will be printed from top down; use rev() to reverse the order.

lwd, lty, lend

Additional parameters to segments(), controlling line style. Use lend = "butt" (the default) if palette is semitransparent, to avoid artefacts.

bty

Character specifying the type of box to be drawn around the legend. The allowed values are "o" (the default) and "n".

cex

Character expansion factor relative to current par("cex").

width

Vector of length two specifying width of legend bar at base and top.

scale

Character string specifying whether width = 1 corresponds to: "pch", the size of a plotting symbol with pch = 1; "lwd", the width of a line with lwd = 1.

col

Colour used for the width bar.

Value

A list, returned invisibly, with components:

• rect A list with components:

  • w, h: positive numbers giving width and height of the legend's box.

  • left, top: x and y coordinates of the upper left corner of the box.

• text: A list with components x, y, numeric vectors of length length(legend), giving the x and y coordinates of the legend's text(s).

Details

This convenience function is not yet very customizable; do file a GitHub issue if you would value additional functionality.

Note that the bg parameter to specify the background colour for the legend box is not presently supported in vertical legends. For use in vertical legends, open a GitHub issue.

Author

Martin R. Smith (martin.smith@durham.ac.uk)

Examples

plot(0:1, 0:1, type = "n", frame.plot = FALSE,
     xlab = "x", ylab = "y")

SpectrumLegend("bottomright", legend = c("Bright", "Middle", "Dark"),
               palette = heat.colors(32L), lwd = 5,
               inset = 0.05, # Inset from plot margin
               title = "Brightness")
SpectrumLegend("topright", horiz = TRUE,
               legend = seq(1, 9, by = 2), palette = 1:8)
SizeLegend(
  "topleft", inset = 0.05, width = c(0, 2),
  title = "Width",
  legend = c("max", ".", ".", "min"),
  palette = topo.colors, # Associate with a colour scale
  y.intersp = 1.5 # Vertical space between labels (also moves title)
)
SizeLegend(
  "bottomleft", horiz = TRUE, width = c(4, 1),
  legend = c("Thick", "Thin"), palette = "darkred",
  inset = 0.06 # Make space for the bar.
               # A future release may calculate this automatically
)