Binning Continuous Data
31 March 2014
Recently, I had a continuous variable that I wanted to plot and use color to show the gradient. The variable’s values were too fine for color to reveal closely spaced data. So I wanted to quantize the variable into defined bands.
The data’s values were outside the (absolute) maximum of the band; I wanted to bucket anything that exceeded the band into the maximum bands. In the future, I’ll change the labels of the interval factor to indicate this.
require(ggplot2)
require(RColorBrewer)
set.seed(1492) #discovery!
sample = data.frame(x = c(1:20), y = 1, obs = runif(20, -150, 150))
the.breaks = seq(-100, 100, by = 20)
sample$interval = factor(findInterval(sample$obs, vec = the.breaks, all.inside = TRUE),
labels = the.breaks, levels = c(1:length(the.breaks)))
pal = rev(brewer.pal(11, "RdBu"))
p = ggplot(sample, aes(x, y, colour = interval))
p = p + geom_point(size = 10)
p = p + scale_colour_manual(values = pal, limits = the.breaks, labels = the.breaks)
p = p + guides(colour = guide_legend(override.aes = list(size = 3, shape = 19)))
p