Returns the variable names corresponding the selected group.
The returned names are the names as they are used by tramME. For example,
when the response is a Surv object, variable.names returns
the name of that object, and not the names of the variables used to create it.
Usage
# S3 method for tramME
variable.names(
object,
which = c("all", "response", "grouping", "shifting", "interacting"),
...
)