Split a Classification Task into Binary Classification Tasks

Splits a classification Task into several binary classification Tasks to perform "One vs. Rest" classification. This works in combination with PipeOpOVRUnite.

For each target level a new binary classification Task is constructed with the respective target level being the positive class and all other target levels being the new negative class "rest".

This PipeOp creates a Multiplicity, which means that subsequent PipeOps are executed multiple times, once for each created binary Task, until a PipeOpOVRUnite is reached.

Note that Multiplicity is currently an experimental features and the implementation or UI may change.

Format

R6Class inheriting from PipeOp.

Construction

PipeOpOVRSplit$new(id = "ovrsplit", param_vals = list())

• id :: character(1)
  Identifier of the resulting object, default "ovrsplit".

• param_vals :: named list
  List of hyperparameter settings, overwriting the hyperparameter settings that would otherwise be set during construction. Default list().

Input and Output Channels

PipeOpOVRSplit has one input channel named "input" taking a TaskClassif both during training and prediction.

PipeOpOVRSplit has one output channel named "output" returning a Multiplicity of TaskClassifs both during training and prediction, i.e., the newly constructed binary classification Tasks.

State

The $state contains the original target levels of the TaskClassif supplied during training.

Parameters

PipeOpOVRSplit has no parameters.

Internals

The original target levels stored in the $state are also used during prediction when creating the new binary classification Tasks.

The names of the element of the output Multiplicity are given by the levels of the target.

If a target level "rest" is present in the input TaskClassif, the negative class will be labeled as "rest." (using as many "."` postfixes needed to yield a valid label).

Should be used in combination with PipeOpOVRUnite.

Fields

Only fields inherited from PipeOp.

Methods

Only methods inherited from PipeOp.

See also

https://mlr-org.com/pipeops.html

Other PipeOps: PipeOp, PipeOpEncodePL, PipeOpEnsemble, PipeOpImpute, PipeOpTargetTrafo, PipeOpTaskPreproc, PipeOpTaskPreprocSimple, mlr_pipeops, mlr_pipeops_adas, mlr_pipeops_blsmote, mlr_pipeops_boxcox, mlr_pipeops_branch, mlr_pipeops_chunk, mlr_pipeops_classbalancing, mlr_pipeops_classifavg, mlr_pipeops_classweights, mlr_pipeops_colapply, mlr_pipeops_collapsefactors, mlr_pipeops_colroles, mlr_pipeops_copy, mlr_pipeops_datefeatures, mlr_pipeops_decode, mlr_pipeops_encode, mlr_pipeops_encodeimpact, mlr_pipeops_encodelmer, mlr_pipeops_encodeplquantiles, mlr_pipeops_encodepltree, mlr_pipeops_featureunion, mlr_pipeops_filter, mlr_pipeops_fixfactors, mlr_pipeops_histbin, mlr_pipeops_ica, mlr_pipeops_imputeconstant, mlr_pipeops_imputehist, mlr_pipeops_imputelearner, mlr_pipeops_imputemean, mlr_pipeops_imputemedian, mlr_pipeops_imputemode, mlr_pipeops_imputeoor, mlr_pipeops_imputesample, mlr_pipeops_kernelpca, mlr_pipeops_learner, mlr_pipeops_learner_pi_cvplus, mlr_pipeops_learner_quantiles, mlr_pipeops_missind, mlr_pipeops_modelmatrix, mlr_pipeops_multiplicityexply, mlr_pipeops_multiplicityimply, mlr_pipeops_mutate, mlr_pipeops_nearmiss, mlr_pipeops_nmf, mlr_pipeops_nop, mlr_pipeops_ovrunite, mlr_pipeops_pca, mlr_pipeops_proxy, mlr_pipeops_quantilebin, mlr_pipeops_randomprojection, mlr_pipeops_randomresponse, mlr_pipeops_regravg, mlr_pipeops_removeconstants, mlr_pipeops_renamecolumns, mlr_pipeops_replicate, mlr_pipeops_rowapply, mlr_pipeops_scale, mlr_pipeops_scalemaxabs, mlr_pipeops_scalerange, mlr_pipeops_select, mlr_pipeops_smote, mlr_pipeops_smotenc, mlr_pipeops_spatialsign, mlr_pipeops_subsample, mlr_pipeops_targetinvert, mlr_pipeops_targetmutate, mlr_pipeops_targettrafoscalerange, mlr_pipeops_textvectorizer, mlr_pipeops_threshold, mlr_pipeops_tomek, mlr_pipeops_tunethreshold, mlr_pipeops_unbranch, mlr_pipeops_updatetarget, mlr_pipeops_vtreat, mlr_pipeops_yeojohnson

Other Multiplicity PipeOps: Multiplicity(), PipeOpEnsemble, mlr_pipeops_classifavg, mlr_pipeops_featureunion, mlr_pipeops_multiplicityexply, mlr_pipeops_multiplicityimply, mlr_pipeops_ovrunite, mlr_pipeops_regravg, mlr_pipeops_replicate

Other Experimental Features: Multiplicity(), mlr_pipeops_multiplicityexply, mlr_pipeops_multiplicityimply, mlr_pipeops_ovrunite, mlr_pipeops_replicate

Examples

library(mlr3)
task = tsk("iris")
po = po("ovrsplit")
po$train(list(task))
#> $output
#> Multiplicity:
#> $setosa
#> 
#> ── <TaskClassif> (150x5): Iris Flowers ─────────────────────────────────────────
#> • Target: Species
#> • Target classes: setosa (positive class, 33%), rest (67%)
#> • Properties: twoclass
#> • Features (4):
#>   • dbl (4): Petal.Length, Petal.Width, Sepal.Length, Sepal.Width
#> 
#> $versicolor
#> 
#> ── <TaskClassif> (150x5): Iris Flowers ─────────────────────────────────────────
#> • Target: Species
#> • Target classes: versicolor (positive class, 33%), rest (67%)
#> • Properties: twoclass
#> • Features (4):
#>   • dbl (4): Petal.Length, Petal.Width, Sepal.Length, Sepal.Width
#> 
#> $virginica
#> 
#> ── <TaskClassif> (150x5): Iris Flowers ─────────────────────────────────────────
#> • Target: Species
#> • Target classes: virginica (positive class, 33%), rest (67%)
#> • Properties: twoclass
#> • Features (4):
#>   • dbl (4): Petal.Length, Petal.Width, Sepal.Length, Sepal.Width
#> 
#> 
po$predict(list(task))
#> $output
#> Multiplicity:
#> $setosa
#> 
#> ── <TaskClassif> (150x5): Iris Flowers ─────────────────────────────────────────
#> • Target: Species
#> • Target classes: setosa (positive class, 33%), rest (67%)
#> • Properties: twoclass
#> • Features (4):
#>   • dbl (4): Petal.Length, Petal.Width, Sepal.Length, Sepal.Width
#> 
#> $versicolor
#> 
#> ── <TaskClassif> (150x5): Iris Flowers ─────────────────────────────────────────
#> • Target: Species
#> • Target classes: versicolor (positive class, 33%), rest (67%)
#> • Properties: twoclass
#> • Features (4):
#>   • dbl (4): Petal.Length, Petal.Width, Sepal.Length, Sepal.Width
#> 
#> $virginica
#> 
#> ── <TaskClassif> (150x5): Iris Flowers ─────────────────────────────────────────
#> • Target: Species
#> • Target classes: virginica (positive class, 33%), rest (67%)
#> • Properties: twoclass
#> • Features (4):
#>   • dbl (4): Petal.Length, Petal.Width, Sepal.Length, Sepal.Width
#> 
#>