data.frame to a ratetable objectdata.frame of population hazards
to an array, and in turn to a ratetable,
which can be used in e.g. longDF2ratetable(DF, value.var = "haz", by.vars = setdiff(names(DF),
value.var))data.frameratetable,
as.data.table.ratetable,
as.data.frame.ratetable