extracat (version 1.7-6)

setcover: greedy setcover optimisation

Description

This function takes an indicator matrix with rows representing objects and columns representing sets and computes a minimal redundancy free set using the greedy setcover optimization algorithm. The aim is to find a minimal set of clusters which covers all objects (or a minimum proportion rat).

Alternatively the number of clusters k can be specified. Then the problem becomes a maximum covergae problem. Both versions also permit weights such as frequencies (weighted setcover/maximum coverage).

Usage

setcover(x, k = NULL, rat = 1, s = NULL, w = NULL, check = TRUE)

Arguments

x

The indicator matrix.

k

An optional number of clusters.

rat

The minimum proportion of objects that is to be covered by the cluster set. If weights are specified in w then those are respected.

s

If weights are specified but not all objects are covered by one of the sets it can be necessary to specify the total weight in order to compute a sensible ratio.

w

Optional weights per object.

check

Whether or not to check for redundancies.

Value

The indices of the clusters in the minimal redundancy-free set. The result is not always the globally optiomal solution since the algorithm is greedy.

See Also

gsac

Examples

# NOT RUN {
# compute 100 clusterings with 24 clusters each:
sc <- scale(olives[,3:10])
km100 <- as.data.frame(replicate(100, kmeans(sc,centers = 24)$cluster))

# convert to indicator matrix
I100 <- idat(km100)

# select from all clusters a minimum set:
scover <- setcover(as.matrix(I100))


cdata <- subtable(
	as.data.frame(cbind(olives[,1:2],
	I100[,scover])),1:(length(scover)+2))
scpcp(cdata,sel="Area")



# }