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\name{specgroups}
\alias{specgroups}
%- Also NEED an `\alias' for EACH other topic documented here.
\title{Average within-group distances for given groups}
\description{
Generates average within-group distances (overall and group-wise) from
a dissimilarity matrix and a given grouping.
}
\usage{
specgroups(distmat,groupvector, groupinfo)
}
%- maybe also `usage' for other objects documented here.
\arguments{
\item{distmat}{dissimilarity matrix or \code{dist}-object.}
\item{groupvector}{integer vector. For every row of \code{distmat},
a number indicating the group membership.}
\item{groupinfo}{list with components \code{lg} (levels of
\code{groupvector}), \code{ng} (number of groups), \code{nsg}
(vector of group sizes).}
}
\value{
A list with parameters
\item{overall}{overall average within-groups dissimilarity.}
\item{gr}{vector of group-wise average within-group dissimilarities
(this will be \code{NaN} if the group size is only 1).}
}
\author{Christian Hennig
\email{christian.hennig@unibo.it}
\url{https://www.unibo.it/sitoweb/christian.hennig/en}}
\examples{
options(digits=4)
data(siskiyou)
x <- prabinit(prabmatrix=siskiyou, neighborhood=siskiyou.nb,
distance="logkulczynski")
groupvector <- as.factor(siskiyou.groups)
ng <- length(levels(groupvector))
lg <- levels(groupvector)
nsg <- numeric(0)
for (i in 1:ng) nsg[i] <- sum(groupvector==lg[i])
groupinfo <- list(lg=lg,ng=ng,nsg=nsg)
specgroups(x$distmat,groupvector,groupinfo)
}
\keyword{cluster}% at least one, from doc/KEYWORDS
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