update.POSIXt() return a date with the specified
elements updated. Elements not specified will be left unaltered. update.Date
and update.POSIXt do not add the specified values to the existing date, they
substitute them for the appropriate parts of the existing date.
# S3 method for POSIXt update( object, ..., roll = FALSE, week_start = getOption("lubridate.week.start", 7), simple = NULL )
a date-time object
named arguments: years, months, ydays, wdays, mdays, days, hours, minutes, seconds, tzs (time zone component)
week starting day (Default is 7, Sunday). Set
logical. Deprecated. Same as
a date object with the requested elements updated. The object will retain its original class unless an element is updated which the original class does not support. In this case, the date returned will be a POSIXlt date object.