Centers all numeric features to mean = 0 (if `center`

parameter is `TRUE`

) and scales them
by dividing them by their root-mean-square (if `scale`

parameter is `TRUE`

).

The root-mean-square here is defined as `sqrt(sum(x^2)/(length(x)-1))`

. If the `center`

parameter
is `TRUE`

, this corresponds to the `sd()`

.

## Format

`R6Class`

object inheriting from `PipeOpTaskPreproc`

/`PipeOp`

.

## Construction

`id`

::`character(1)`

Identifier of resulting object, default`"scale"`

.`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

Input and output channels are inherited from `PipeOpTaskPreproc`

.

The output is the input `Task`

with all affected numeric parameters centered and/or scaled.

## State

The `$state`

is a named `list`

with the `$state`

elements inherited from `PipeOpTaskPreproc`

, as well as:

`center`

::`numeric`

The mean / median (depending on`robust`

) of each numeric feature during training, or 0 if`center`

is`FALSE`

. Will be subtracted during the predict phase.`scale`

::`numeric`

The value by which features are divided. 1 if`scale`

is`FALSE`

If`robust`

is`FALSE`

, this is the root mean square, defined as`sqrt(sum(x^2)/(length(x)-1))`

, of each feature, possibly after centering. If`robust`

is`TRUE`

, this is the mean absolute deviation multiplied by 1.4826 (see stats::mad of each feature, possibly after centering. This is 1 for features that are constant during training if`center`

is`TRUE`

, to avoid division-by-zero.

## Parameters

The parameters are the parameters inherited from `PipeOpTaskPreproc`

, as well as:

`center`

::`logical(1)`

Whether to center features, i.e. subtract their`mean()`

from them. Default`TRUE`

.`scale`

::`logical(1)`

Whether to scale features, i.e. divide them by`sqrt(sum(x^2)/(length(x)-1))`

. Default`TRUE`

.`robust`

::`logical(1)`

Whether to use robust scaling; instead of scaling / centering with mean / standard deviation, median and median absolute deviation`mad`

are used. Initialized to`FALSE`

.

## Internals

Imitates the `scale()`

function for `robust = FALSE`

and alternatively subtracts the
`median`

and divides by `mad`

for `robust = TRUE`

.

## Methods

Only methods inherited from `PipeOpTaskPreproc`

/`PipeOp`

.

## See also

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

Other PipeOps:
`PipeOp`

,
`PipeOpEnsemble`

,
`PipeOpImpute`

,
`PipeOpTargetTrafo`

,
`PipeOpTaskPreproc`

,
`PipeOpTaskPreprocSimple`

,
`mlr_pipeops`

,
`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_encode`

,
`mlr_pipeops_encodeimpact`

,
`mlr_pipeops_encodelmer`

,
`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_missind`

,
`mlr_pipeops_modelmatrix`

,
`mlr_pipeops_multiplicityexply`

,
`mlr_pipeops_multiplicityimply`

,
`mlr_pipeops_mutate`

,
`mlr_pipeops_nmf`

,
`mlr_pipeops_nop`

,
`mlr_pipeops_ovrsplit`

,
`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_scalemaxabs`

,
`mlr_pipeops_scalerange`

,
`mlr_pipeops_select`

,
`mlr_pipeops_smote`

,
`mlr_pipeops_spatialsign`

,
`mlr_pipeops_subsample`

,
`mlr_pipeops_targetinvert`

,
`mlr_pipeops_targetmutate`

,
`mlr_pipeops_targettrafoscalerange`

,
`mlr_pipeops_textvectorizer`

,
`mlr_pipeops_threshold`

,
`mlr_pipeops_tunethreshold`

,
`mlr_pipeops_unbranch`

,
`mlr_pipeops_updatetarget`

,
`mlr_pipeops_vtreat`

,
`mlr_pipeops_yeojohnson`

## Examples

```
library("mlr3")
task = tsk("iris")
pos = po("scale")
pos$train(list(task))[[1]]$data()
#> Species Petal.Length Petal.Width Sepal.Length Sepal.Width
#> <fctr> <num> <num> <num> <num>
#> 1: setosa -1.3357516 -1.3110521 -0.89767388 1.01560199
#> 2: setosa -1.3357516 -1.3110521 -1.13920048 -0.13153881
#> 3: setosa -1.3923993 -1.3110521 -1.38072709 0.32731751
#> 4: setosa -1.2791040 -1.3110521 -1.50149039 0.09788935
#> 5: setosa -1.3357516 -1.3110521 -1.01843718 1.24503015
#> ---
#> 146: virginica 0.8168591 1.4439941 1.03453895 -0.13153881
#> 147: virginica 0.7035638 0.9192234 0.55148575 -1.27867961
#> 148: virginica 0.8168591 1.0504160 0.79301235 -0.13153881
#> 149: virginica 0.9301544 1.4439941 0.43072244 0.78617383
#> 150: virginica 0.7602115 0.7880307 0.06843254 -0.13153881
one_line_of_iris = task$filter(13)
one_line_of_iris$data()
#> Species Petal.Length Petal.Width Sepal.Length Sepal.Width
#> <fctr> <num> <num> <num> <num>
#> 1: setosa 1.4 0.1 4.8 3
pos$predict(list(one_line_of_iris))[[1]]$data()
#> Species Petal.Length Petal.Width Sepal.Length Sepal.Width
#> <fctr> <num> <num> <num> <num>
#> 1: setosa -1.335752 -1.442245 -1.259964 -0.1315388
```