ArchiveBatchFSelect {mlr3fselect}

Class for Logging Evaluated Feature Sets

Description

The ArchiveBatchFSelect stores all evaluated feature sets and performance scores.

Details

The ArchiveBatchFSelect is a container around a data.table::data.table(). Each row corresponds to a single evaluation of a feature set. See the section on Data Structure for more information. The archive stores additionally a mlr3::BenchmarkResult (⁠$benchmark_result⁠) that records the resampling experiments. Each experiment corresponds to a single evaluation of a feature set. The table (⁠$data⁠) and the benchmark result (⁠$benchmark_result⁠) are linked by the uhash column. If the archive is passed to as.data.table(), both are joined automatically.

Data structure

The table (⁠$data⁠) has the following columns:

• One column for each feature of the task (⁠$search_space⁠).

• One column for each performance measure (⁠$codomain⁠).

• runtime_learners (numeric(1))
  Sum of training and predict times logged in learners per mlr3::ResampleResult / evaluation. This does not include potential overhead time.

• timestamp (POSIXct)
  Time stamp when the evaluation was logged into the archive.

• batch_nr (integer(1))
  Feature sets are evaluated in batches. Each batch has a unique batch number.

• uhash (character(1))
  Connects each feature set to the resampling experiment stored in the mlr3::BenchmarkResult.

Analysis

For analyzing the feature selection results, it is recommended to pass the archive to as.data.table(). The returned data table is joined with the benchmark result which adds the mlr3::ResampleResult for each feature set.

The archive provides various getters (e.g. ⁠$learners()⁠) to ease the access. All getters extract by position (i) or unique hash (uhash). For a complete list of all getters see the methods section.

The benchmark result (⁠$benchmark_result⁠) allows to score the feature sets again on a different measure. Alternatively, measures can be supplied to as.data.table().

S3 Methods

• as.data.table.ArchiveBatchFSelect(x, exclude_columns = "uhash", measures = NULL)
  Returns a tabular view of all evaluated feature sets.
  ArchiveBatchFSelect -> data.table::data.table()
  

  • x (ArchiveBatchFSelect)

  • exclude_columns (character())
    Exclude columns from table. Set to NULL if no column should be excluded.

  • measures (list of mlr3::Measure)
    Score feature sets on additional measures.

Super classes

bbotk::Archive -> bbotk::ArchiveBatch -> ArchiveBatchFSelect

Public fields

benchmark_result

(mlr3::BenchmarkResult)
Benchmark result.

Active bindings

ties_method

(character(1))
Method to handle ties.

Methods

Public methods

• ArchiveBatchFSelect$new()

• ArchiveBatchFSelect$learner()

• ArchiveBatchFSelect$learners()

• ArchiveBatchFSelect$predictions()

• ArchiveBatchFSelect$resample_result()

• ArchiveBatchFSelect$print()

• ArchiveBatchFSelect$best()

• ArchiveBatchFSelect$clone()

Inherited methods

• bbotk::Archive$format()
• bbotk::Archive$help()
• bbotk::ArchiveBatch$add_evals()
• bbotk::ArchiveBatch$clear()
• bbotk::ArchiveBatch$nds_selection()

Method new()

Creates a new instance of this R6 class.

Usage

ArchiveBatchFSelect$new(
  search_space,
  codomain,
  check_values = TRUE,
  ties_method = "least_features"
)

Arguments

search_space

(paradox::ParamSet)
Search space. Internally created from provided mlr3::Task by instance.

codomain

(bbotk::Codomain)
Specifies codomain of objective function i.e. a set of performance measures. Internally created from provided mlr3::Measures by instance.

check_values

(logical(1))
If TRUE (default), hyperparameter configurations are check for validity.

ties_method

(character(1))
The method to break ties when selecting sets while optimizing and when selecting the best set. Can be "least_features" or "random". The option "least_features" (default) selects the feature set with the least features. If there are multiple best feature sets with the same number of features, one is selected randomly. The random method returns a random feature set from the best feature sets. Ignored if multiple measures are used.

Method learner()

Retrieve mlr3::Learner of the i-th evaluation, by position or by unique hash uhash. i and uhash are mutually exclusive. Learner does not contain a model. Use ⁠$learners()⁠ to get learners with models.

Usage

ArchiveBatchFSelect$learner(i = NULL, uhash = NULL)

Arguments

i

(integer(1))
The iteration value to filter for.

uhash

(logical(1))
The uhash value to filter for.

Method learners()

Retrieve list of trained mlr3::Learner objects of the i-th evaluation, by position or by unique hash uhash. i and uhash are mutually exclusive.

Usage

ArchiveBatchFSelect$learners(i = NULL, uhash = NULL)

Arguments

i

(integer(1))
The iteration value to filter for.

uhash

(logical(1))
The uhash value to filter for.

Method predictions()

Retrieve list of mlr3::Prediction objects of the i-th evaluation, by position or by unique hash uhash. i and uhash are mutually exclusive.

Usage

ArchiveBatchFSelect$predictions(i = NULL, uhash = NULL)

Arguments

i

(integer(1))
The iteration value to filter for.

uhash

(logical(1))
The uhash value to filter for.

Method resample_result()

Retrieve mlr3::ResampleResult of the i-th evaluation, by position or by unique hash uhash. i and uhash are mutually exclusive.

Usage

ArchiveBatchFSelect$resample_result(i = NULL, uhash = NULL)

Arguments

i

(integer(1))
The iteration value to filter for.

uhash

(logical(1))
The uhash value to filter for.

Method print()

Printer.

Usage

ArchiveBatchFSelect$print()

Arguments

...

(ignored).

Method best()

Returns the best scoring feature sets.

Usage

ArchiveBatchFSelect$best(batch = NULL, ties_method = NULL)

Arguments

batch

(integer())
The batch number(s) to limit the best results to. Default is all batches.

ties_method

(character(1))
Method to handle ties. If NULL (default), the global ties method set during initialization is used. The default global ties method is least_features which selects the feature set with the least features. If there are multiple best feature sets with the same number of features, one is selected randomly. The random method returns a random feature set from the best feature sets.

Returns

data.table::data.table()

Method clone()

The objects of this class are cloneable with this method.

Usage

ArchiveBatchFSelect$clone(deep = FALSE)

Arguments

deep

Whether to make a deep clone.