While I was studying Hierarchical Agglomerative Clustering in the book Elements of Statistical Learning in the chapter Unsupervised Learning, I came through the following :
The statement
The clusters produced by single linkage can violate the “compactness” property that all observations within each cluster tend to be similar to one another, based on the supplied observation dissimilarities {dii'}.
how is violating the "compactness"? How does single linkage produce clusters with very large diameters?
It will tend to produce compact clusters with small diameters
And how does "complete linkage cluster" produce compact clusters with small diameters?
These things are not making any sense to me.