Apply borderline-SMOTE AlgorithmSource:
step_bsmote() creates a specification of a recipe step that generate new
examples of the minority class using nearest neighbors of these cases in the
border region between classes.
A recipe object. The step will be added to the sequence of operations for this recipe.
One or more selector functions to choose which variable is used to sample the data. See
selections()for more details. The selection should result in single factor variable. For the
tidymethod, these are not currently used.
Not used by this step since no new variables are created.
A logical to indicate if the quantities for preprocessing have been estimated.
A character string of the variable name that will be populated (eventually) by the
A numeric value for the ratio of the majority-to-minority frequencies. The default value (1) means that all other levels are sampled up to have the same frequency as the most occurring level. A value of 0.5 would mean that the minority levels will have (at most) (approximately) half as many rows than the majority level.
An integer. Number of nearest neighbor that are used to generate the new examples of the minority class.
Type of two borderline-SMOTE method. Defaults to FALSE. See details.
A logical. Should the step be skipped when the recipe is baked by
bake()? While all operations are baked when
prep()is run, some operations may not be able to be conducted on new data (e.g. processing the outcome variable(s)). Care should be taken when using
skip = TRUEas it may affect the computations for subsequent operations.
An integer that will be used as the seed when smote-ing.
A character string that is unique to this step to identify it.
An updated version of
recipe with the new step
added to the sequence of existing steps (if any). For the
tidy method, a tibble with columns
terms which is
the variable used to sample.
This methods works the same way as
step_smote(), expect that instead of
generating points around every point of of the minority class each point is
first being classified into the boxes "danger" and "not". For each point the
k nearest neighbors is calculated. If all the neighbors comes from a
different class it is labeled noise and put in to the "not" box. If more then
half of the neighbors comes from a different class it is labeled "danger.
If all_neighbors = FALSE then points will be generated between nearest neighbors in its own class. If all_neighbors = TRUE then points will be generated between any nearest neighbors. See examples for visualization.
neighbors controls the way the new examples are created.
For each currently existing minority class example X new examples will be
created (this is controlled by the parameter
over_ratio as mentioned
above). These examples will be generated by using the information from the
neighbors nearest neighbor of each example of the minority class.
neighbors controls how many of these neighbor are used.
All columns used in this step must be numeric with no missing data.
When used in modeling, users should strongly consider using the
skip = TRUE so that the extra sampling is not
conducted outside of the training set.
tidy() this step, a tibble with columns
(the selectors or variables selected) will be returned.
This step has 3 tuning parameters:
over_ratio: Over-Sampling Ratio (type: double, default: 1)
neighbors: # Nearest Neighbors (type: integer, default: 5)
all_neighbors: All Neighbors (type: logical, default: FALSE)
Hui Han, Wen-Yuan Wang, and Bing-Huan Mao. Borderline-smote: a new over-sampling method in imbalanced data sets learning. In International Conference on Intelligent Computing, pages 878–887. Springer, 2005.
library(recipes) library(modeldata) data(hpc_data) hpc_data0 <- hpc_data %>% select(-protocol, -day) orig <- count(hpc_data0, class, name = "orig") orig #> # A tibble: 4 × 2 #> class orig #> <fct> <int> #> 1 VF 2211 #> 2 F 1347 #> 3 M 514 #> 4 L 259 up_rec <- recipe(class ~ ., data = hpc_data0) %>% # Bring the minority levels up to about 1000 each # 1000/2211 is approx 0.4523 step_bsmote(class, over_ratio = 0.4523) %>% prep() training <- up_rec %>% bake(new_data = NULL) %>% count(class, name = "training") training #> # A tibble: 4 × 2 #> class training #> <fct> <int> #> 1 VF 2211 #> 2 F 1347 #> 3 M 1000 #> 4 L 1000 # Since `skip` defaults to TRUE, baking the step has no effect baked <- up_rec %>% bake(new_data = hpc_data0) %>% count(class, name = "baked") baked #> # A tibble: 4 × 2 #> class baked #> <fct> <int> #> 1 VF 2211 #> 2 F 1347 #> 3 M 514 #> 4 L 259 # Note that if the original data contained more rows than the # target n (= ratio * majority_n), the data are left alone: orig %>% left_join(training, by = "class") %>% left_join(baked, by = "class") #> # A tibble: 4 × 4 #> class orig training baked #> <fct> <int> <int> <int> #> 1 VF 2211 2211 2211 #> 2 F 1347 1347 1347 #> 3 M 514 1000 514 #> 4 L 259 1000 259 library(ggplot2) ggplot(circle_example, aes(x, y, color = class)) + geom_point() + labs(title = "Without SMOTE") recipe(class ~ x + y, data = circle_example) %>% step_bsmote(class, all_neighbors = FALSE) %>% prep() %>% bake(new_data = NULL) %>% ggplot(aes(x, y, color = class)) + geom_point() + labs(title = "With borderline-SMOTE, all_neighbors = FALSE") recipe(class ~ x + y, data = circle_example) %>% step_bsmote(class, all_neighbors = TRUE) %>% prep() %>% bake(new_data = NULL) %>% ggplot(aes(x, y, color = class)) + geom_point() + labs(title = "With borderline-SMOTE, all_neighbors = TRUE")