makeMulticlassWrapper: Fuse learner with multiclass method.
In riebetob/mlr: Machine Learning in R

Description Usage Arguments Value See Also

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.

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

`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”.