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Encapsulate a Graph as a Learner

Source: R/GraphLearner.R
mlr_learners_graph.Rd

A Learner that encapsulates a Graph to be used in mlr3 resampling and benchmarks.

The Graph must return a single Prediction on its $predict() call. The result of the $train() call is discarded, only the internal state changes during training are used.

The predict_type of a GraphLearner can be obtained or set via it's predict_type active binding. Setting a new predict type will try to set the predict_type in all relevant PipeOp / Learner encapsulated within the Graph. Similarly, the predict_type of a Graph will always be the smallest denominator in the Graph.

A GraphLearner is always constructed in an untrained state. When the graph argument has a non-NULL $state, it is ignored.

Format

R6Class object inheriting from mlr3::Learner.

Construction

GraphLearner$new(graph, id = NULL, param_vals = list(), task_type = NULL, predict_type = NULL)

  • graph :: Graph | PipeOp
    Graph to wrap. Can be a PipeOp, which is automatically converted to a Graph. This argument is usually cloned, unless clone_graph is FALSE; to access the Graph inside GraphLearner by-reference, use $graph.

  • id :: character(1) Identifier of the resulting Learner.

  • param_vals :: named list
    List of hyperparameter settings, overwriting the hyperparameter settings . Default list().

  • task_type :: character(1)
    What task_type the GraphLearner should have; usually automatically inferred for Graphs that are simple enough.

  • predict_type :: character(1)
    What predict_type the GraphLearner should have; usually automatically inferred for Graphs that are simple enough.

  • clone_graph :: logical(1)
    Whether to clone graph upon construction. Unintentionally changing graph by reference can lead to unexpected behaviour, so TRUE (default) is recommended. In particular, note that the $state of $graph is set to NULL by reference on construction of GraphLearner, during $train(), and during $predict() when clone_graph is FALSE.

Fields

Fields inherited from PipeOp, as well as:

  • graph :: Graph
    Graph that is being wrapped. This field contains the prototype of the Graph that is being trained, but does not contain the model. Use graph_model to access the trained Graph after $train(). Read-only.

  • graph_model :: Learner
    Graph that is being wrapped. This Graph contains a trained state after $train(). Read-only.

Internals

as_graph() is called on the graph argument, so it can technically also be a list of things, which is automatically converted to a Graph via gunion(); however, this will usually not result in a valid Graph that can work as a Learner. graph can furthermore be a Learner, which is then automatically wrapped in a Graph, which is then again wrapped in a GraphLearner object; this usually only adds overhead and is not recommended.

See also

Other Learners: mlr_learners_avg

Examples

 if (requireNamespace("rpart")) { 
library("mlr3")

graph = po("pca") %>>% lrn("classif.rpart")

lr = GraphLearner$new(graph)
lr = as_learner(graph)  # equivalent

lr$train(tsk("iris"))

lr$graph$state  # untrained version!
# The following is therefore NULL:
lr$graph$pipeops$classif.rpart$learner_model$model

# To access the trained model from the PipeOpLearner's Learner, use:
lr$graph_model$pipeops$classif.rpart$learner_model$model

# Feature importance (of principal components):
lr$graph_model$pipeops$classif.rpart$learner_model$importance()
 } 
#>       PC1       PC2       PC3       PC4 
#> 85.795455 18.016529  5.694731  3.254132