bsmote {themis}

borderline-SMOTE Algorithm

Description

BSMOTE generates generate new examples of the minority class using nearest neighbors of these cases in the border region between classes.

Usage

bsmote(df, var, k = 5, over_ratio = 1, all_neighbors = FALSE)

Arguments

df

data.frame or tibble. Must have 1 factor variable and remaining numeric variables.

var

Character, name of variable containing factor variable.

k

An integer. Number of nearest neighbor that are used to generate the new examples of the minority class.

over_ratio

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.

all_neighbors

Type of two borderline-SMOTE method. Defaults to FALSE. See details.

Details

This methods works the same way as 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.

The parameter 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. The parameter neighbors controls how many of these neighbor are used.

All columns used in this step must be numeric with no missing data.

Value

A data.frame or tibble, depending on type of df.

References

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.

See Also

step_bsmote() for step function of this method

Other Direct Implementations: adasyn(), nearmiss(), smotenc(), smote(), tomek()

Examples

circle_numeric <- circle_example[, c("x", "y", "class")]

res <- bsmote(circle_numeric, var = "class")

res <- bsmote(circle_numeric, var = "class", k = 10)

res <- bsmote(circle_numeric, var = "class", over_ratio = 0.8)

res <- bsmote(circle_numeric, var = "class", all_neighbors = TRUE)