Combine continuous and discrete color scale in ggplot2?

Question

I am a ggplot2 newbie. I am making a scatter plot where the points are colored based on a third continuous variable. However, for some of the points, that continuous variable has either an Inf value or a NaN. How can I generate a continuous scale that has a special, separate color for Inf and another separate color for NaN?

One way to get this behavior is to subset the data, and make a separate layer for the special points, where the color is set. But I'd like the special colors to enter the legend as well, and think it would be cleaner to eliminate the need to subset the data.

Thanks! Uri

Chase · Accepted Answer · 2011-08-28 22:29:02Z

I'm sure this can be made more efficient, but here's one approach. Essentially, we follow your advice of subsetting the data into the different parts, divide the continuous data into discrete bins, then patch everything back together and use a scale of our own choosing.

library(ggplot2) library(RColorBrewer) #Sample data dat <- data.frame(x = rnorm(100), y = rnorm(100), z = rnorm(100)) dat[sample(nrow(dat), 5), 3] <- NA dat[sample(nrow(dat), 5), 3] <- Inf #Subset out the real values dat.good <- dat[!(is.na(dat$z)) & is.finite(dat$z) ,] #Create 6 breaks for them dat.good$col <- cut(dat.good$z, 6) #Grab the bad ones dat.bad <- dat[is.na(dat$z) | is.infinite(dat$z) ,] dat.bad$col <- as.character(dat.bad$z) #Rbind them back together dat.plot <- rbind(dat.good, dat.bad) #Make your own scale with RColorBrewer yourScale <- c(brewer.pal(6, "Blues"), "red","green") ggplot(dat.plot, aes(x,y, colour = col)) + geom_point() + scale_colour_manual("Intensity", values = yourScale)

enter image description here

Why does dat$col[is.finite(dat$z)] <- cut(dat$z[is.finite(dat$z)],6) fail to work? Instead of getting interval labels, I just get integers...
@Uri - I ran into the same issue and thus went down the path of separating out the "good" values from the bad, then binding them back together at the end. I'm guessing it's because when you try to do it at once, the factors are converted to their numeric equivalent...though I admittedly didn't spend that much time trying to force it to work as the solution I came up with worked.

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