Better way to define a data.table (implement using structure)

implementDF.R

# Usecases: 
# when creating many R environments and each have independent data-set

ll <- list(
  as.factor(c(2001, 2002, 2004, 2006)),
  I(c(2001, 2002, 2004, 2006)),
  ordered(c(2001, 2002, 2004, 2006)),
  as.double(c(366.3240, 365.4124, 366.5323423, 364.9573234)),
  list(list(letters), list(LETTERS), list(), list())
)

dd3 <- structure(
  .Data = ll,
  .Names = c("year", "AsIs Year","yearO", "length of days", "more"),
  .typeOf = c("factor", "numeric", "ordered","numeric", "list"),
  row.names = c(NA, -4L),
  class = "data.frame",
  comment = "Ordered YearO for categorical analysis and other variables"
)
dd3

attributes(dd3)