R/diverge0.R

In stevenpawley/Diverge0:

diverge0 <- function(p, ramp, rev=F) {
  # p: a trellis object resulting from rasterVis::levelplot
  # ramp: the name of an RColorBrewer palette (as character), a character
  #       vector of colour names to interpolate, or a colorRampPalette.
  require(RColorBrewer)
  require(rasterVis)

  if(length(ramp)==1 && is.character(ramp) && ramp %in%
     row.names(brewer.pal.info)) {
    ramp = ifelse(rev==F, suppressWarnings(colorRampPalette(brewer.pal(11, ramp))),
                  suppressWarnings(colorRampPalette(rev(brewer.pal(11, ramp)))))
  } else if(length(ramp) > 1 && is.character(ramp) && all(ramp %in% colors())) {
    ramp = ifelse(rev==F, colorRampPalette(ramp), rev(colorRampPalette(ramp)))
  } else if(!is.function(ramp))
    stop('ramp should be either the name of a RColorBrewer palette, ',
         'a vector of colours to be interpolated, or a colorRampPalette.')

  rng <- range(p$legend[[1]]$args$key$at)
  s <- seq(-max(abs(rng)), max(abs(rng)), len=1001)
  i <- findInterval(rng[which.min(abs(rng))], s)
  zlim <- switch(which.min(abs(rng)), `1`=i:(1000+1), `2`=1:(i+1))
  p$legend[[1]]$args$key$at <- s[zlim]
  p$par.settings$regions$col <- ramp(1000)[zlim[-length(zlim)]]
  p
}