Draw dendrogram using agglomerative algorithm

Question

I have tried making it dendrogram but it was seeming to me very wrong.

Pair I have made: XB, XBZ, XBZY

Answer 1

The obvious problem is, that your distance matrix is inconsistent.

If the distence from A to B is 3 and the distance from B to Y is 2, how is it possible that the distance from A to Y is 6?

If you slightly adapt your matrix, so that it corresponds to a distance of points in a real space, you get better results.

Example Using R

data <- c(0,3,3.3,1,3,
          3,0,3.3,1,3,
          3.3,3.3,0,3,6,         
          1,1,3,0,3, 
          3,3,6,3,0)          

dim_names <- c("X","Z","Y","B","A")
mat <- matrix(data,nrow=5,ncol=5,byrow=TRUE, dimnames = list(dim_names,dim_names) )

dist <- as.dist(mat)

dist

    X   Z   Y   B
Z 3.0            
Y 3.3 3.3        
B 1.0 1.0 3.0    
A 3.0 3.0 6.0 3.0

hc <- hclust(dist)

plot(hc, hang = -1)

which produce