[R] changing the ordering of leaves in a dendrogram

[White.Denis@epamail.epa.gov]

> I'd like to change the way plot.hclust displays an hclust object.
Here's
> a description of how it's done now, from the R documentation of
hclust:
>
>      In hierarchical cluster displays, a decision is needed at each
merge
>      to specify which subtree should go on the left and which on the
right.
>      Since, for n observations there are n-1 merges, there are
2^{(n-1)}
>      possible orderings for the leaves in a cluster tree, or
dendrogram.
>      The algorithm used in hclust is to order the subtree so that the
>      tighter cluster is on the left (the last, i.e. most recent, merge
>      of the left subtree is at a lower value than the last merge of
the
>      right subtree). Single observations are the tightest clusters
possible,
>      and merges involving two observations place them in order by
their
>      observation sequence number.
>
> I have a factor vector (if that's the right term) for the
observations, and
> I'd like to order the display of the leaves so that leaves of the same
> level are grouped together as much as possible.  Even something as
simple
> as putting the higher average code on the left would help.
>
> I've spent some time looking at the code in rpart, but I'm having a
hard
> time figuring out what I need to modify.  Or maybe someone's already
done
> something similar?  Any help much appreciated!
>
>    David Marimont
>    NXP Data Analysis, Inc.
>    http://www.nxpdata.com

You could look at function group.clust in contributed package maptree
for possible ideas.

Denis White
   US EPA, 200 SW 35th St, Corvallis, Oregon, 97333 USA
   voice: 541.754.4476, email: white.denis at epa.gov
   web: www.epa.gov/wed/pages/staff/white/

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