r - Clustering list for hclust function

Question

Using plot(hclust(dist(x))) method, I was able to draw a cluster tree map. It works. Yet I would like to get a list of all clusters, not a tree diagram, because I have huge amount of data (like 150K nodes) and the plot gets messy.

In other words, lets say if a b c is a cluster and if d e f g is a cluster then I would like to get something like this:

1 a,b,c
2 d,e,f,g

Please note that this is not exactly what I want to get as an "output". It is just an example. I just would like to be able to get a list of clusters instead of a tree plot It could be vector, matrix or just simple numbers that show which groups elements belong to.

How is this possible?

Answer 1

I will use the dataset available in R to demonstrate how to cut a tree into desired number of pieces. Result is a table.

Construct a hclust object.

hc <- hclust(dist(USArrests), "ave")
#plot(hc)

You can now cut the tree into as many branches as you want. For my next trick, I will split the tree into two groups. You set the number of cuts with the k parameter. See ?cutree and the use of paramter h which may be more useful to you (see cutree(hc, k = 2) == cutree(hc, h = 110)).

cutree(hc, k = 2)
       Alabama         Alaska        Arizona       Arkansas     California 
             1              1              1              2              1 
      Colorado    Connecticut       Delaware        Florida        Georgia 
             2              2              1              1              2 
        Hawaii          Idaho       Illinois        Indiana           Iowa 
             2              2              1              2              2 
        Kansas       Kentucky      Louisiana          Maine       Maryland 
             2              2              1              2              1 
 Massachusetts       Michigan      Minnesota    Mississippi       Missouri 
             2              1              2              1              2 
       Montana       Nebraska         Nevada  New Hampshire     New Jersey 
             2              2              1              2              2 
    New Mexico       New York North Carolina   North Dakota           Ohio 
             1              1              1              2              2 
      Oklahoma         Oregon   Pennsylvania   Rhode Island South Carolina 
             2              2              2              2              1 
  South Dakota      Tennessee          Texas           Utah        Vermont 
             2              2              2              2              2 
      Virginia     Washington  West Virginia      Wisconsin        Wyoming 
             2              2              2              2              2