aggregate               Aggregate data based on given grouping.
correlation_threshold   Remove redundant variables.
count_na_rows           Count the number of 'NA's per variable.
drop_na_columns         Remove variables with NA values.
drop_na_rows            Drop rows that are 'NA' in all variables.
generalized_log         Generalized log transform data.
normalize               Normalize observation variables.
replicate_correlation   Measure replicate correlation of variables.
transform               Transform observation variables.
variable_importance     Measure variable importance.
variable_select         Select observation variables.
variance_threshold      Remove variables with near-zero variance.
