Clustering: Hierarchical Clustering

### Hierarchical Clustering
hc <- hclust(dist(USArrests), method="average", members=NULL)
# Cluster linkage methods:
#  "ward"
#  "single"
#  "complete"
#  "average"
#  "mcquitty"
#  "median"
#  "centroid"
summary(hc)

## plot Cluster Dendrogram
plot(hc, hang=-1, labels=abbreviate(row.names(USArrests),2), cex=0.8) # ?plclust()
rect.hclust(hc, k=5, border="red") # 在圖中框出各群



# Cutting the dendrogram to form k=5 clusters here:
groups <- cutree(hc, k=5) # cut tree into 5 clusters