predict.kohonen: Predict properties using a trained Kohonen map

In kohonen: Supervised and Unsupervised Self-Organising Maps

Predict properties using a trained Kohonen map

Description

Map objects to a trained Kohonen map, and return for each object the desired property associated with the corresponding winning unit. These properties may be provided explicitly (argument unit.predictions) or implicitly (by providing trainingdata, that will be mapped to the SOM - the averages of the winning units for the trainingdata then will be used as unit.predictions). If not given at all, the codebook vectors of the map will be used.

Usage

## S3 method for class 'kohonen'
predict(object,
                          newdata = NULL,
                          unit.predictions = NULL,
                          trainingdata = NULL,
                          whatmap = NULL,
                          threshold = 0,
                          maxNA.fraction = object$maxNA.fraction,
                          ...)

Arguments

object	Trained network, containing one or more information layers.
newdata	List of data matrices, or one single data matrix, for which predictions are to be made. The data layers should match those in the trained map. If not presented, the training data in the map will be used. No data.frame objects are allowed.
unit.predictions	Explicit definition of the predictions for each unit. Should be a list of matrices, vectors or factors, of the same length as object$codes.
trainingdata	List of data matrices, or one single data matrix, determining the mapping of the training data. Normally, data stored in the kohonen object will be used for this, but one can also specify this argument explicitly. Layers should match the trained map.
whatmap, maxNA.fraction	parameters that usually will be taken from the x object, but can be supplied by the user as well. See supersom for more information.
threshold	Used in converting class predictions back into factors; see classmat2classvec.
...	Further arguments to be passed to map.kohonen, in particular user.weights. If not provided will be taken from object.

Details

The new data are mapped to the trained SOM using the layers indicated by the whatmap argument. The predictions correspond to the unit.predictions, normally corresponding to the averages of the training data mapping to individual units. If no unit.predictions are provided, the trainingdata will be used to calculate them - if trainingdata is not provided by the user and the kohonen object contains data, these will be used. If no objects of the training data are mapping to a particular unit, the prediction for that unit will be NA.

Value

Returns a list with components

prediction	predicted values for the properties of interest. When multiple values are predicted, this element is a list, otherwise a vector or a matrix.
unit.classif	vector of unit numbers to which objects in the newdata object are mapped.
unit.predictions	prediction values associated with map units. Again, when multiple properties are predicted, this is a list.
whatmap	the numbers of the data layers in the kohonen object used in the mapping on which the predictions are based.

Author(s)

Ron Wehrens

See Also

som,xyf, supersom, map

Examples

data(wines)

training <- sample(nrow(wines), 120)
Xtraining <- scale(wines[training, ])
Xtest <- scale(wines[-training, ],
               center = attr(Xtraining, "scaled:center"),
               scale = attr(Xtraining, "scaled:scale"))
trainingdata <- list(measurements = Xtraining,
                     vintages = vintages[training])
testdata <- list(measurements = Xtest, vintages = vintages[-training])

mygrid = somgrid(5, 5, "hexagonal")
som.wines <- supersom(trainingdata, grid = mygrid)

## ################################################################
## Situation 0: obtain expected values for training data (all layers,
## also if not used in training) on the basis of the position in the map
som.prediction <- predict(som.wines)

## ################################################################
## Situation 1: obtain predictions for all layers used in training

som.prediction <- predict(som.wines, newdata = testdata)
table(vintages[-training], som.prediction$predictions[["vintages"]])


## ################################################################
## Situation 2: obtain predictions for the vintage based on the mapping
## of the sample characteristics only. There are several ways of doing this:

som.prediction <- predict(som.wines, newdata = testdata,
                          whatmap = "measurements")
table(vintages[-training], som.prediction$predictions[["vintages"]])

## same, but now indicated implicitly
som.prediction <- predict(som.wines, newdata = testdata[1])
table(vintages[-training], som.prediction$predictions[["vintages"]])

## if no names are present in the list elements whatmap needs to be
## given explicitly; note that the order of the data layers needs to be
## consistent with the kohonen object
som.prediction <- predict(som.wines, newdata = list(Xtest), whatmap = 1)
table(vintages[-training], som.prediction$predictions[["vintages"]])

## for xyf: explicitly indicate which layer is to be used for the mapping
xyf.wines <- xyf(Xtraining, vintages[training], grid = mygrid)
xyf.prediction <- predict(xyf.wines, Xtest, whatmap = 1)
table(vintages[-training], xyf.prediction$predictions[[2]])

## ###############################################################
## Situation 3: predictions for layers not present in the original
## data. Training data need to be provided for those layers.
som.wines <- supersom(Xtraining, grid = mygrid)
som.prediction <- predict(som.wines, newdata = testdata,
                          trainingdata = trainingdata)
table(vintages[-training], som.prediction$predictions[["vintages"]])

## ################################################################
## yeast examples, including NA values

data(yeast)
training.indices <- sample(nrow(yeast$alpha), 300)
training <- rep(FALSE, nrow(yeast$alpha))
training[training.indices] <- TRUE

## unsupervised mapping, based on the alpha layer only. Prediction
## for all layers including alpha
yeast.som <- supersom(lapply(yeast, function(x) subset(x, training)),
                      somgrid(4, 6, "hexagonal"),
                      whatmap = "alpha", maxNA.fraction = .5)
yeast.som.prediction <-
  predict(yeast.som,
          newdata = lapply(yeast, function(x) subset(x, !training)))

table(yeast$class[!training], yeast.som.prediction$prediction[["class"]])

## ################################################################
## supervised mapping - creating the map is now based on both
## alpha and class, prediction for class based on the mapping of alpha.
yeast.som2 <- supersom(lapply(yeast, function(x) subset(x, training)),
                       grid = somgrid(4, 6, "hexagonal"),
                       whatmap = c("alpha", "class"), maxNA.fraction = .5)
yeast.som2.prediction <-
  predict(yeast.som2,
          newdata = lapply(yeast, function(x) subset(x, !training)),
          whatmap = "alpha")
table(yeast$class[!training], yeast.som2.prediction$prediction[["class"]])

kohonen documentation built on July 9, 2023, 7:40 p.m.