Under-samples the majority classes by replacing them with cluster representatives found with k-means.
Arguments
- df
data.frame or tibble. Must have 1 factor variable and remaining numeric variables.
- var
Character, name of variable containing factor variable.
- under_ratio
A numeric value for the ratio of the majority-to-minority frequencies. The default value (1) means that all other levels are sampled down to have the same frequency as the least occurring level. A value of 2 would mean that the majority levels will have (at most) (approximately) twice as many rows than the minority level.
A named numeric vector can be used instead to give different levels different targets, for example
c(a = 2, b = 3). The names must be levels of the outcome and the values are ratios of the minority level, exactly as in the single-number case. Levels that are not named are left untouched, as are rows with a missing outcome. Because a vector of targets is not a single value, supplying one means this argument can no longer be tuned. Seevignette("ratio", package = "themis")for more details.- voting
A character string. Either
"soft"(the default) to use the cluster centroids themselves, or"hard"to use the observation closest to each centroid.
Details
Each class larger than the target count is summarized by running k-means on the observations of that class, using as many clusters as the target count. The class is then replaced by one representative per cluster:
voting = "soft"the cluster centroids themselves are used, so the returned observations are synthetic points that need not appear in the input.
voting = "hard"the observation closest to each centroid is used, so all returned observations are real rows. The representative is always picked from the class being under-sampled.
This makes it the one prototype generation under-sampler in this package. The other under-sampling methods perform prototype selection, keeping a subset of the original rows.
Because two clusters can share the same closest observation, voting = "hard" can return slightly fewer observations than the target count.
All columns used in this function must be numeric with no missing data.
See also
step_cluster_centroids() for step function of this method
Other Direct Implementations:
adasyn(),
bsmote(),
cnn(),
enn(),
instance_hardness(),
kmeans_smote(),
ncl(),
nearmiss(),
oss(),
rose(),
smogn(),
smote(),
smoten(),
smotenc(),
svmsmote(),
tomek()
Examples
circle_numeric <- circle_example[, c("x", "y", "class")]
res <- cluster_centroids(circle_numeric, var = "class")
res <- cluster_centroids(circle_numeric, var = "class", voting = "hard")
res <- cluster_centroids(circle_numeric, var = "class", under_ratio = 1.5)