groupedData creates groupedData objects.
  convertFromS3groupedData converts older S3 style objects of the
  same class name used in the nlme package.groupedData(formula, data,
            order.groups = TRUE,
            FUN = function(x, ...) max(x, na.rm = TRUE),
            outer = NULL, inner = NULL,
            labels = list(), units = list(), ...)
convertFromS3groupedData(from)nlmedata with additional attributes.nlme docs for now. order.groups, FUN are currently
  ignored.