week_of_year.RdWeek of Year
week(date = today(), iso = FALSE, ...)logical if FALSE the first week starts on year-01-01 so that all years have 53 weeks and
all days will fall in the week whatever the year (corresponds to POSIX %W).
if TRUE the first week starts on a Monday (week_start == 1) and contains
that year's first Thursday (min_days == 4) so that a year can have 52 or 53 weeks
(corresponds to POSIX %V).
Further arguments for year_first