Hi all,

I've been doing some investigation to see if it is possible to implement an 
hclust/dendrogram related requirement that I've been given. So far ?hclust and 
a lot of googling haven't provided the information I'm looking for (I've been 
using R sporadically for a year).

The requirement I have is to:
On a dendrogram plot, draw points at various merge locations, based on some 
other data. For instance, for an initial 15 cluster dend, assume I need to mark 
the 1st,2nd and 7th merge by drawing points on the plot. This needs to be done 
within an R script, though if some FORTRAN or C code needs to be modified, that 
is fine.


Where I'm stuck is:
1) making sense of the full $merge in hclust
2) programatically calculating an X-coordinate for plotting the marker points.

For 1) The first couple of merges in make sense as they correspond to known 
clusters. But after several merges, the values in $merge do not seem to 
correspond to anything. eg. After a merge, what/how is the 'new' cluster 
referred to? This results is not knowing what needs to be done to 
programatically locate where on the plot the merge at height 'h' is.

At this stage I'm assuming part of this lies in the 2 external FORTRAN 
functions that hclust calls. Any assistance on how to determine the merge 
location on the plot would be great!

Thanks,



Ben

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