feat: store ranger oob error without storing models (#357)

* feat: store ranger oob error without storing models

* ...

Author: be-marc

R/LearnerClassifRanger.R

@@ -112,10 +112,15 @@ LearnerClassifRanger = R6Class("LearnerClassifRanger",
     #'
     #' @return `numeric(1)`.
     oob_error = function() {
-      if (is.null(self$model)) {
-        stopf("No model stored")
+      if (!is.null(self$state$oob_error)) {
+        return(self$state$oob_error)
       }
-      self$model$prediction.error
+
+      if (!is.null(self$model)) {
+        return(self$model$prediction.error)
+      }
+
+      stopf("No model stored")
     },
 
     #' @description
@@ -162,6 +167,10 @@ LearnerClassifRanger = R6Class("LearnerClassifRanger",
       model = self$model
       model$num.trees = self$param_set$values$num.trees
       model
+    },
+
+    .extract_oob_error = function() {
+      self$model$prediction.error
     }
   )
 )

R/LearnerRegrRanger.R

@@ -92,12 +92,17 @@ LearnerRegrRanger = R6Class("LearnerRegrRanger",
     #' @description
     #' The out-of-bag error, extracted from model slot `prediction.error`.
     #'
-    #' @return `numeric(1)`.
+    #' @return `numeric(1)`
     oob_error = function() {
-      if (is.null(self$model)) {
-        stopf("No model stored")
+      if (!is.null(self$state$oob_error)) {
+        return(self$state$oob_error)
       }
-      self$model$prediction.error
+
+      if (!is.null(self$model)) {
+        return(self$model$prediction.error)
+      }
+
+      stopf("No model stored")
     },
 
     #' @description
@@ -155,6 +160,10 @@ LearnerRegrRanger = R6Class("LearnerRegrRanger",
       model = self$models
       model$num.trees = self$param_set$values$num.trees
       model
+    },
+
+    .extract_oob_error = function() {
+      self$model$prediction.error
     }
   )
 )

tests/testthat/test_classif_ranger.R

@@ -97,3 +97,12 @@ test_that("selected_features", {
   learner$train(task)
   expect_set_equal(learner$selected_features(), c("Sepal.Length", "Sepal.Width", "Petal.Length", "Petal.Width"))
 })
+
+test_that("oob_error available without stored model", {
+  task = tsk("pima")
+  learner = lrn("classif.ranger")
+
+  rr = resample(task, learner, rsmp("holdout"), store_models = FALSE)
+
+  expect_number(rr$aggregate(msr("oob_error")))
+})

tests/testthat/test_regr_ranger.R

@@ -96,3 +96,12 @@ test_that("selected_features", {
   learner$train(task)
   expect_set_equal(learner$selected_features(), c("am", "cyl", "wt"))
 })
+
+test_that("oob_error available without stored model", {
+  task = tsk("mtcars")
+  learner = lrn("regr.ranger")
+
+  rr = resample(task, learner, rsmp("holdout"), store_models = FALSE)
+
+  expect_number(rr$aggregate(msr("oob_error")))
+})