[R] Package: clue; Function: consensus; Question: element weights for criterion functions

[Bruno L. Giordano]

Dear R community and Kurt,

I am using consensus.r from clue to compute hard consensus partitions 
(method: "hard/euclidean"; same considerations apply for "hard/manhattan").

The function gives in output a hard consensus partition that minimizes a 
criterion measure Crit, namely the sum of the weighted dissimilarities 
between the input partitions on the one hand, and the consensus 
partition on the other.

I would like to have an exact value for Crit (consensus.r only shows 
approximate values when verbose=TRUE).

To this purpose, I manually compute Crit using the cl_dissimilarity 
function from the same package.

The problem I have is that the Crit I compute manually differs widely 
from that computed by criterion.r (compare "Minimum" with "Manually 
computed criterion" after running the sample code).

I figure the difference arises because my criterion measure does not 
weight the cases.

However, I wonder:

1. why does the consensus partition search algorithm have to weight the 
cases? Is the weighting part of the heuristic?

2. how can I recover these weights (hacking consensus.r is not really 
straightforward, since it includes many subfunctions)?

3. is there something wrong in my R code (pasted below)?

Thank you for any suggestion, and for this very helpful package.

Best,

	Bruno

p.s. in the code, you can set nnruns to 1 if you do not want to load 
your machine.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Bruno L. Giordano, Ph.D.
Music Perception and Cognition Laboratory
CIRMMT http://www.cirmmt.mcgill.ca/
Schulich School of Music, McGill University
555 Sherbrooke Street West
Montréal, QC H3A 1E3
Canada
Office: +1 514 398 4535 ext. 00900
http://www.music.mcgill.ca/~bruno/


###################### CODE #############################

library(clue)

##### partitions
p1=c(1,2,3,4,5,6,7,8,9,1,1,2,2,3,3,4,4,1,1,2,2,3,3,4,4)
p2=c(1,1,2,2,3,3,4,4,1,1,2,2,3,3,4,4,1,1,2,2,3,3,4,4,1)
p3=c(1,1,2,2,3,3,4,4,1,1,2,2,3,3,4,4,1,1,2,2,3,3,4,5,5)

##### partitions ensemble
p=as.cl_ensemble(list(as.cl_partition(p1),as.cl_partition(p2),as.cl_partition(p3)))

##### control parameters
nclasses=9
nnruns=50
contr=list(verbose=TRUE,nruns=nnruns,k=nclasses)
meth="hard/euclidean"

##### fit consensus partition
pcons=cl_consensus(p,method=meth,control=contr)
print(pcons)

##### compute unweighted criterion measure
Crit=rep(0,length(p))
for (i in 1:length(p))
{
     tmp=cl_dissimilarity(pcons,p[[i]],method="euclidean")
     Crit[i]=tmp[[1]]
}

cat("Manually computed criterion: ")
cat(as.character(sum(Crit)))