flexmix {flexmix} | R Documentation

## Flexible Mixture Modeling

### Description

FlexMix implements a general framework for finite mixtures of regression models. Parameter estimation is performed using the EM algorithm: the E-step is implemented by `flexmix`, while the user can specify the M-step.

### Usage

    flexmix(formula, data = list(), k = NULL, cluster = NULL,
            model=NULL, concomitant=NULL, control = NULL,
            weights = NULL)
    ## S4 method for signature 'flexmix':
    summary(object, eps=1e-4, ...)

### Arguments

`formula` | A symbolic description of the model to be fit. The general form is `y~x|g` where `y` is the response, `x` the set of predictors and `g` an optional grouping factor for repeated measurements.
`data` | An optional data frame containing the variables in the model.
`k` | Number of clusters (not needed if `cluster` is specified).
`cluster` | Either a matrix with `k` columns of initial cluster membership probabilities for each observation; or a factor or integer vector with the initial cluster assignments of observations at the start of the EM algorithm. Default is random assignment into `k` clusters.
`weights` | An optional vector of weights to be used in the fitting process. Should be 'NULL', a numeric vector or a formula.
`model` | Object of class `FLXM` or list of `FLXM` objects. Default is the object returned by calling `FLXMRglm()`.
`concomitant` | Object of class `FLXP`. Default is the object returned by calling `FLXPconstant`.
`control` | Object of class `FLXcontrol` or a named list.
`object` | Object of class `flexmix`.
`eps` | Probabilities below this threshold are treated as zero in the summary method.
`...` | Currently not used.

### Details

FlexMix models are described by objects of class `FLXM`, which in turn are created by driver functions like `FLXMRglm` or `FLXMCmvnorm`. Multivariate responses with independent components can be specified using a list of `FLXM` objects.

The `summary` method lists for each component the prior probability, the number of observations assigned to the corresponding cluster, the number of observations with a posterior probability larger than `eps` and the ratio of the latter two numbers (which indicates how separated the cluster is from the others).

### Value

Returns an object of class `flexmix`.

### Author(s)

Friedrich Leisch and Bettina Gruen

### References

Friedrich Leisch. FlexMix: A general framework for finite mixture models and latent class regression in R. Journal of Statistical Software, 11(8), 2004. http://www.jstatsoft.org/v11/i08/

### See Also

`plot-methods`

### Examples

    data("NPreg")

    ## mixture of two linear regression models. Note that control parameters
    ## can be specified as named list and abbreviated if unique.
    ex1 <- flexmix(yn~x+I(x^2), data=NPreg, k=2,
                       control=list(verb=5, iter=100))

    ex1
    summary(ex1)
    plot(ex1)

    ## now we fit a model with one Gaussian response and one Poisson
    ## response. Note that the formulas inside the call to FLXMRglm are
    ## relative to the overall model formula.
    ex2 <- flexmix(yn~x, data=NPreg, k=2,
                   model=list(FLXMRglm(yn~.+I(x^2)),
                              FLXMRglm(yp~., family="poisson")))
    plot(ex2)

    ex2
    table(ex2@cluster, NPreg$class)

    ## for Gaussian responses we get coefficients and standard deviation
    parameters(ex2, component=1, model=1)

    ## for Poisson response we get only coefficients
    parameters(ex2, component=1, model=2)

    ## fitting a model only to the Poisson response is of course
    ## done like this
    ex3 <- flexmix(yp~x, data=NPreg, k=2, model=FLXMRglm(family="poisson"))

    ## if observations are grouped, i.e., we have several observations per
    ## individual, fitting is usually much faster:
    ex4 <- flexmix(yp~x|id1, data=NPreg, k=2,
                   model=FLXMRglm(family="poisson"))

    ## And now a binomial example. Mixtures of binomials are not generically
    ## identified, here the grouping variable is necessary:
    set.seed(1234)
    ex5 <- stepFlexmix(cbind(yb,1-yb)~x, data=NPreg, k=2,
                       model=FLXMRglm(family="binomial"), nrep=5)
    table(NPreg$class, clusters(ex5))

    ex6 <- stepFlexmix(cbind(yb,1-yb)~x|id2, data=NPreg, k=2,
                       model=FLXMRglm(family="binomial"), nrep=5)
    table(NPreg$class, clusters(ex6))

[Package flexmix version 2.2-4 Index]