R: Fuse learner with multiclass method.

makeMulticlassWrapper {mlr} | R Documentation

## Fuse learner with multiclass method.

### Description

Fuses a base learner with a multi-class method. Creates a learner object, which can be used like any other learner object. This way learners which can only handle binary classification will be able to handle multi-class problems, too.

We use a multiclass-to-binary reduction principle, where multiple binary problems are created from the multiclass task. How these binary problems are generated is defined by an error-correcting-output-code (ECOC) code book. This also allows the simple and well-known one-vs-one and one-vs-rest approaches. Decoding is currently done via Hamming decoding, see e.g. here http://jmlr.org/papers/volume11/escalera10a/escalera10a.pdf.

Currently, the approach always operates on the discrete predicted labels of the binary base models (instead of their probabilities) and the created wrapper cannot predict posterior probabilities.

### Usage

    makeMulticlassWrapper(learner, mcw.method = "onevsrest")

### Arguments

`learner` | (Learner | `character(1)`) The learner. If you pass a string the learner will be created via makeLearner.
`mcw.method` | (`character(1)` | `function`) “onevsone” or “onevsrest”. You can also pass a function, with signature `function(task)` and which returns a ECOC codematrix with entries +1,-1,0. Columns define new binary problems, rows correspond to classes (rows must be named). 0 means class is not included in binary problem. Default is “onevsrest”.

### Value

Learner.

### See Also

Other wrapper: `makeBaggingWrapper()`, `makeClassificationViaRegressionWrapper()`, `makeConstantClassWrapper()`, `makeCostSensClassifWrapper()`, `makeCostSensRegrWrapper()`, `makeDownsampleWrapper()`, `makeDummyFeaturesWrapper()`, `makeExtractFDAFeatsWrapper()`, `makeFeatSelWrapper()`, `makeFilterWrapper()`, `makeImputeWrapper()`, `makeMultilabelBinaryRelevanceWrapper()`, `makeMultilabelClassifierChainsWrapper()`, `makeMultilabelDBRWrapper()`, `makeMultilabelNestedStackingWrapper()`, `makeMultilabelStackingWrapper()`, `makeOverBaggingWrapper()`, `makePreprocWrapperCaret()`, `makePreprocWrapper()`, `makeRemoveConstantFeaturesWrapper()`, `makeSMOTEWrapper()`, `makeTuneWrapper()`, `makeUndersampleWrapper()`, `makeWeightedClassesWrapper()`

[Package mlr version 2.17.1 Index]