Changes the components of a date objectSource:
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.
a date-time object
named arguments: years, months, ydays, wdays, mdays, days, hours, minutes, seconds, tzs (time zone component)
is a string vector of length one or two. When two values are supplied they specify how to roll date-times when they fall into "skipped" and "repeated" DST transitions respectively. A single value is replicated to the length of two. Possible values are:
* `pre` - Use the time before the transition boundary. * `boundary` - Use the time exactly at the boundary transition. * `post` - Use the time after the boundary transition. * `xfirst` - crossed-first: First time which occurred when crossing the boundary. For addition with positive units pre interval is crossed first and- post interval last. With negative units post interval is crossed first, pre last. For subtraction the logic is reversed.* `xlast` - crossed-last. * `NA` - Produce NAs when the resulting time falls inside the problematic interval.
For example `roll_dst = c("NA", "pre") indicates that for skiped intervals return NA and for repeated times return the earlier time.
When multiple units are supplied the meaning of "negative period" is determined by the largest unit. For example
time_add(t, days = -1, hours = 2, roll_dst = "xfirst")would operate as if with negative period, thus crossing the boundary from the "post" to "pre" side and "xfirst" and hence resolving to "post" time. As this might result in confusing behavior. See examples.
"xfirst" and "xlast" make sense for addition and subtraction only. An error is raised if an attempt is made to use them with other functions.
week start day (Default is 7, Sunday. Set
lubridate.week.startto override). Full or abbreviated names of the days of the week can be in English or as provided by the current locale.
- simple, roll
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.