S7 bundles S3 definitions for key S3 classes provided by the base packages:
class_data.frame for data frames.
class_Date for dates.
class_factor for factors.
class_POSIXct, class_POSIXlt and class_POSIXt for date-times.
class_formula for formulas.
class_factorclass_Date
class_POSIXct
class_POSIXlt
class_POSIXt
class_data.frame
class_formula