ddalphaf.train: Functional DD-Classifier

In ddalpha: Depth-Based Classification and Calculation of Data Depth

Functional DD-Classifier

Description

Trains the functional DD-classifier

Usage

ddalphaf.train(dataf, labels, subset, 
                adc.args = list(instance = "avr", 
                               numFcn = -1, 
                               numDer = -1), 
                classifier.type = c("ddalpha", "maxdepth", "knnaff", "lda", "qda"), 
                cv.complete = FALSE, 
                maxNumIntervals = min(25, ceiling(length(dataf[[1]]$args)/2)),
                seed = 0,
                ...)

Arguments

dataf	list containing lists (functions) of two vectors of equal length, named "args" and "vals": arguments sorted in ascending order and corresponding them values respectively
labels	list of output labels of the functional observations
subset	an optional vector specifying a subset of observations to be used in training the classifier.
adc.args	Represents a function sample as a multidimensional (dimension="numFcn"+"numDer") one averaging (instance = "avr") or evaluating (instance = "val") for that each function and it derivative on "numFcn" (resp. "numDer") equal nonoverlapping covering intervals First two named "args" and "vals" are arguments sorted in ascending order and having same bounds for all functions and corresponding them values respectively instance type of discretizing the functions: "avr" - by averaging over intervals of the same length "val" - by taking values on equally-spaced grid numFcn number of function intervals numDer number of first-derivative intervals Set numFcn and numDer to -1 to apply cross-validation. Set adc.args to a list of "adc.args" objects to cross-validate only over these values.
classifier.type	the classifier which is used on the transformed space. The default value is 'ddalpha'.
cv.complete	T: apply complete cross-validation F: restrict cross-validation by Vapnik-Chervonenkis bound
maxNumIntervals	maximal number of intervals for cross-validation ( max(numFcn + numDer) = maxNumIntervals )
seed	the random seed. The default value seed=0 makes no changes.
...	additional parameters, passed to the classifier, selected with parameter classifier.type.

Details

The functional DD-classifier is fast nonparametric procedure for classifying functional data. It consists of a two-step transformation of the original data plus a classifier operating on a low-dimensional hypercube. The functional data are first mapped into a finite-dimensional location-slope space and then transformed by a multivariate depth function into the DD-plot, which is a subset of the unit hypercube. This transformation yields a new notion of depth for functional data. Three alternative depth functions are employed for this, as well as two rules for the final classification. The resulting classifier is cross-validated over a small range of parameters only, which is restricted by a Vapnik-Cervonenkis bound. The entire methodology does not involve smoothing techniques, is completely nonparametric and allows to achieve Bayes optimality under standard distributional settings. It is robust and efficiently computable.

Value

Trained functional DD-classifier

References

Mosler, K. and Mozharovskyi, P. (2017). Fast DD-classification of functional data. Statistical Papers 58 1055–1089.

Mozharovskyi, P. (2015). Contributions to Depth-based Classification and Computation of the Tukey Depth. Verlag Dr. Kovac (Hamburg).

See Also

ddalphaf.classify for classification using functional DDα-classifier, compclassf.train to train the functional componentwise classifier, dataf.* for functional data sets included in the package.

Examples

## Not run: 

## load the Growth dataset
dataf = dataf.growth()

learn = c(head(dataf$dataf, 49), tail(dataf$dataf, 34))
labels= c(head(dataf$labels, 49), tail(dataf$labels, 34)) 
test  = tail(head(dataf$dataf, 59), 10)    # elements 50:59. 5 girls, 5 boys

#cross-validate over the whole variants up to dimension 3
c1 = ddalphaf.train (learn, labels, classifier.type = "ddalpha", maxNumIntervals = 3)

classified1 = ddalphaf.classify(c1, test)

print(unlist(classified1))
print(c1$adc.args) 

# cross-validate over these two variants
c2 = ddalphaf.train (learn, labels, classifier.type = "ddalpha", 
                     adc.args = list(
                       list(instance = "avr", 
                            numFcn = 1, 
                            numDer = 2),
                       list(instance = "avr", 
                            numFcn = 0, 
                            numDer = 2)))

classified2 = ddalphaf.classify(c2, test)

print(unlist(classified2))
print(c2$adc.args) 


## End(Not run)

ddalpha documentation built on March 23, 2022, 9:07 a.m.