Re: Are these bugs in cluster?

[Alan Mead]

John suggested that I post to pspp-dev.  I'm adding code to the k-means
(i.e., quick-cluster.c) procedure to show cluster membership.

CLUSTER works perfectly on a trivial two-dimensional problem but it
fails miserably on some real data. For example, in one analysis
requesting 3 clusters on 98 cases, it found that everyone was in cluster
3 and zero people were in clusters 1 & 2.  I think part of it is that
the starting values seem to be a pattern of 1's and zero's, even though
the comments describe selecting random individuals as starting values.

My question is about accessing the data.  I copied other code to use a
"casereader" to iterate over the rows of data. Below are the relevant
parts of the code I've added that seems to display cluster membership.
If I want to randomly select cases as starting values, is there a way to
retrieve random records directly?

-Alan

quick_cluster_show_membership (struct Kmeans *kmeans, const struct
casereader *reader, const struct qc *qc)
{
[...]
  struct ccase *c;
  struct casereader *cs = casereader_clone (reader);
[...]
  for (i = 0; (c = casereader_read (cs)) != NULL; i++, case_unref (c))
[...]


-- 

Alan D. Mead, Ph.D.
President, Talent Algorithms Inc.

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