Question

I have a situation in which i am plotting a dendrogram with data points that come with class labels.
I wish to see that agglomerative clustering groups those with the same label together. Color coding the labels makes it easy to read such a dendrogram. Is there a way we can achieve this with ggdendro in R ?

Answer 1

Stealing most of the setup from this post …

library(ggplot2)
library(ggdendro)
data(mtcars)
x <- as.matrix(scale(mtcars))
dd.row <- as.dendrogram(hclust(dist(t(x))))
ddata_x <- dendro_data(dd.row)

p2 <- ggplot(segment(ddata_x)) +
  geom_segment(aes(x=x, y=y, xend=xend, yend=yend))

… and adding a grouping factor …

labs <- label(ddata_x)
labs$group <- c(rep("Clust1", 5), rep("Clust2", 2), rep("Clust3", 4))
labs
#     x y text  group
# 1   1 0 carb Clust1
# 2   2 0   wt Clust1
# 3   3 0   hp Clust1
# 4   4 0  cyl Clust1
# 5   5 0 disp Clust1
# 6   6 0 qsec Clust2
# 7   7 0   vs Clust2
# 8   8 0  mpg Clust3
# 9   9 0 drat Clust3
# 10 10 0   am Clust3
# 11 11 0 gear Clust3

… you can use the aes(colour=) argument to geom_text() to color your labels:

p2 + geom_text(data=label(ddata_x),
               aes(label=label, x=x, y=0, colour=labs$group))

(If you want to supply your own colors, you can use scale_colour_manual(), doing something like this:

p2 + geom_text(data=label(ddata_x),
               aes(label=label, x=x, y=0, colour=labs$group)) +
     scale_colour_manual(values=c("blue", "orange", "darkgreen"))