Class Dendrogram

object --+    
         |    
Clustering --+
             |
            Dendrogram

Known Subclasses:

• VertexDendrogram

The hierarchical clustering (dendrogram) of some dataset.

A hierarchical clustering means that we know not only the way the elements are separated into groups, but also the exact history of how individual elements were joined into larger subgroups.

This class internally represents the hierarchy by a matrix with n rows and 2 columns -- or more precisely, a list of lists of size 2. This is exactly the same as the original format used by igraph's C core. The ith row of the matrix contains the indices of the two clusters being joined in time step i. The joint group will be represented by the ID n+i, with i starting from one. The ID of the joint group will be referenced in the upcoming steps instead of any of its individual members. So, IDs less than or equal to n (where n is the number of rows in the matrix) mean the original members of the dataset (with ID from 0 to n), while IDs up from n+1 mean joint groups. As an example, take a look at the dendrogram and the internal representation of a given clustering of five nodes:

 0 -+
    |
 1 -+-+
      |
 2 ---+-+        <====>   [[0, 1], [3, 4], [2, 5], [6, 7]]
        |
 3 -+   |
    |   |
 4 -+---+---