Elegant code for quantile colour mapping in ggplot2, and a less elegant function to make pretty legend labels

ggplot_quantile_colours.R

require(ggplot2)
require(stringr)

d = as.vector(round(abs(10 * sapply(1:4, function(n)rnorm(20, mean=n, sd=.6)))))

ggplot(data=NULL, aes(x=1:length(d), y=d, col=cut(d,quantile(d)))) + 
  geom_point(size=5) + scale_colour_manual(values=rainbow(5))

quantile_labels = function(d, qtls, units, round=2, minzero=F, maxplus=F, space=T){
  labs = levels(cut(d, qtls,include.lowest=T))
  for(i in c('[/(]', '[/[]', ']')) labs = stringr::str_replace_all(labs, i, '')
  labs = stringr::str_split(labs, ',')
  labs = lapply(labs, function(i) i = round(as.numeric(i), round))
  if(minzero) labs[[1]][1] = '0'
  labs = unlist(lapply(labs, function(i) i = paste(i, collapse='-')))
  if(maxplus) labs[[length(labs)]] = stringr::str_replace(labs[[length(labs)]], '-[0-9]+', '+')
  if(space) labs = paste(labs, units) else labs = paste0(labs, units)
  labs
}

qtls = quantile(d, probs = seq(0, 1, length.out=5))
quantile_labels(d, qtls, 'eggs')
quantile_labels(d, qtls, '%', round=0, space=F)

col_labs = quantile_labels(d, qtls, '%', round=0, space=F, minzero=T, maxplus=T)

ggplot(data=NULL, aes(x=1:length(d), y=d, col=cut(d,quantile(d)))) + geom_point(size=5) + 
  scale_colour_manual(name = "Data quantile", values=rev(rainbow(4)), labels = col_labs) +
  guides(col = guide_legend(reverse = TRUE))