kernlab (version 0.9-13)

kkmeans: Kernel k-means

Description

A weighted kernel version of the famous k-means algorithm.

Usage

## S3 method for class 'formula':
kkmeans(x, data = NULL, na.action = na.omit, ...)

## S3 method for class 'matrix': kkmeans(x, centers, kernel = "rbfdot", kpar = "automatic", alg="kkmeans", p=1, na.action = na.omit, ...)

## S3 method for class 'kernelMatrix': kkmeans(x, centers, ...)

## S3 method for class 'list': kkmeans(x, centers, kernel = "stringdot", kpar = list(length=4, lambda=0.5), alg ="kkmeans", p = 1, na.action = na.omit, ...)

Arguments

x
the matrix of data to be clustered, or a symbolic description of the model to be fit, or a kernel Matrix of class kernelMatrix, or a list of character vectors.
data
an optional data frame containing the variables in the model. By default the variables are taken from the environment which `kkmeans' is called from.
centers
Either the number of clusters or a matrix of initial cluster centers. If the first a random initial partitioning is used.
kernel
the kernel function used in training and predicting. This parameter can be set to any function, of class kernel, which computes a inner product in feature space between two vector arguments (see link{kernels}). kernlab
kpar
a character string or the list of hyper-parameters (kernel parameters). The default character string "automatic" uses a heuristic the determine a suitable value for the width parameter of the RBF kernel. A list can also be used contai
alg
the algorithm to use. Options currently include kkmeans and kerninghan.
p
a parameter used to keep the affinity matrix positive semidefinite
na.action
The action to perform on NA
...
additional parameters

Value

  • An S4 object of class specc which extends the class vector containing integers indicating the cluster to which each point is allocated. The following slots contain useful information
  • centersA matrix of cluster centers.
  • sizeThe number of point in each cluster
  • withinssThe within-cluster sum of squares for each cluster
  • kernelfThe kernel function used

Details

kernel k-means uses the 'kernel trick' (i.e. implicitly projecting all data into a non-linear feature space with the use of a kernel) in order to deal with one of the major drawbacks of k-means that is that it cannot capture clusters that are not linearly separable in input space. The algorithm is implemented using the triangle inequality to avoid unnecessary and computational expensive distance calculations. This leads to significant speedup particularly on large data sets with a high number of clusters. With a particular choice of weights this algorithm becomes equivalent to Kernighan-Lin, and the norm-cut graph partitioning algorithms. The function also support input in the form of a kernel matrix or a list of characters for text clustering. The data can be passed to the kkmeans function in a matrix or a data.frame, in addition kkmeans also supports input in the form of a kernel matrix of class kernelMatrix or as a list of character vectors where a string kernel has to be used.

References

Inderjit Dhillon, Yuqiang Guan, Brian Kulis A Unified view of Kernel k-means, Spectral Clustering and Graph Partitioning UTCS Technical Report http://www.cs.utexas.edu/users/kulis/pubs/spectral_techreport.pdf

See Also

specc, kpca, kcca

Examples

Run this code
## Cluster the iris data set.
data(iris)

sc <- kkmeans(as.matrix(iris[,-5]), centers=3)

sc
centers(sc)
size(sc)
withinss(sc)

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