| cmeans {e1071} | R Documentation |
The fuzzy version of the known kmeans clustering algorithm as well as an on-line variant (Unsupervised Fuzzy Competitive learning).
cmeans(x, centers, iter.max = 100, verbose = FALSE,
dist = "euclidean", method = "cmeans", m = 2,
rate.par = NULL, weights = 1, control = list())
x |
The data matrix where columns correspond to variables and rows to observations. |
centers |
Number of clusters or initial values for cluster centers. |
iter.max |
Maximum number of iterations. |
verbose |
If TRUE, make some output during learning. |
dist |
Must be one of the following: If "euclidean", the
mean square error, if "manhattan", the mean absolute error is
computed. Abbreviations are also accepted. |
method |
If "cmeans", then we have the c-means fuzzy
clustering method, if "ufcl" we have the on-line update.
Abbreviations are also accepted. |
m |
A number greater than 1 giving the degree of fuzzification. |
rate.par |
A number between 0 and 1 giving the parameter of the learning rate for the on-line variant. The default corresponds to 0.3. |
weights |
a numeric vector with non-negative case weights.
Recycled to the number of observations in x if necessary. |
control |
a list of control parameters. See Details. |
The data given by x is clustered by generalized versions of the
fuzzy c-means algorithm, which use either a fixed-point or an
on-line heuristic for minimizing the objective function
sum_i sum_j w_i u_{ij}^m d_{ij},
where w_i is the weight of observation i, u_{ij} is
the membership of observation i in cluster j, and
d_{ij} is the distance (dissimilarity) between observation
i and center j. The dissimilarities used are the sums of
squares ("euclidean") or absolute values ("manhattan")
of the elementwise differences.
If centers is a matrix, its rows are taken as the initial cluster
centers. If centers is an integer, centers rows of
x are randomly chosen as initial values.
The algorithm stops when the maximum number of iterations (given by
iter.max) is reached, or when the algorithm is unable to reduce
the current value val of the objective function by
reltol * (abs(val) * reltol) at a step. The relative
convergence tolerance reltol can be specified as the
reltol component of the list of control parameters, and
defaults to sqrt(.Machine$double.eps).
If verbose is TRUE, each iteration displays its number
and the value of the objective function.
If method is "cmeans", then we have the c-means
fuzzy clustering method, see for example Bezdek (1981). If
"ufcl", we have the On-line Update (Unsupervised Fuzzy
Competitive Learning) method due to Chung and Lee (1992), see also Pal
et al (1996). This method works by performing an update directly
after each input signal (i.e., for each single observation).
The parameters m defines the degree of fuzzification. It is
defined for real values greater than 1 and the bigger it is the more
fuzzy the membership values of the clustered data points are.
An object of class "fclust" which is a list with components:
centers |
the final cluster centers. |
size |
the number of data points in each cluster of the closest hard clustering. |
cluster |
a vector of integers containing the indices of the clusters where the data points are assigned to for the closest hard clustering, as obtained by assigning points to the (first) class with maximal membership. |
iter |
the number of iterations performed. |
membership |
a matrix with the membership values of the data points to the clusters. |
withinerror |
the value of the objective function. |
call |
the call used to create the object. |
Evgenia Dimitriadou and Kurt Hornik
J. C. Bezdek (1981). Pattern recognition with fuzzy objective function algorithms. New York: Plenum.
Fu Lai Chung and Tong Lee (1992). Fuzzy competitive learning. Neural Networks, 7(3), 539–551.
Nikhil R. Pal, James C. Bezdek, and Richard J. Hathaway (1996). Sequential competitive learning and the fuzzy c-means clustering algorithms. Neural Networks, 9(5), 787–796.
# a 2-dimensional example
x<-rbind(matrix(rnorm(100,sd=0.3),ncol=2),
matrix(rnorm(100,mean=1,sd=0.3),ncol=2))
cl<-cmeans(x,2,20,verbose=TRUE,method="cmeans",m=2)
print(cl)
# a 3-dimensional example
x<-rbind(matrix(rnorm(150,sd=0.3),ncol=3),
matrix(rnorm(150,mean=1,sd=0.3),ncol=3),
matrix(rnorm(150,mean=2,sd=0.3),ncol=3))
cl<-cmeans(x,6,20,verbose=TRUE,method="cmeans")
print(cl)