In hierarchical clustering, the two most similar clusters are combined and continue to combine until all objects are in the same cluster. Hierarchical clustering produces a tree called a dendrogram that shows the hierarchy of the clusters.
To show this concept, let's start by looking at the dataset called animals embedded in the R package called cluster:
> library(cluster)
> data(animals)
> dim(animals)
[1] 20 6
> head(animals)
war fly ver end gro hai
ant 1 1 1 1 2 1
bee 1 2 1 1 2 2
cat 2 1 2 1 1 2
cpl 1 1 1 1 1 2
chi 2 1 2 2 2 2
cow 2 1 2 1 2 2
> colnames(animals)
[1] "war" "fly" "ver" "end" "gro" "hai"
> apply(animals,2, table) # simple overview
war fly ver end gro hai
1 10 16 6 12 6 11
2 10 4 14 6 11 9
In total, ...
