Add and subtract months to a date without exceeding the last day of the new month
Adding months frustrates basic arithmetic because consecutive months have
different lengths. With other elements, it is helpful for arithmetic to
perform automatic roll over. For example, 12:00:00 + 61 seconds becomes
12:01:01. However, people often prefer that this behavior NOT occur with
months. For example, we sometimes want January 31 + 1 month = February 28 and
not March 3. %m+% performs this type of arithmetic. Date %m+% months(n)
always returns a date in the nth month after Date. If the new date would
usually spill over into the n + 1th month, %m+% will return the last day of
the nth month (rollback()). Date %m-% months(n) always returns a
date in the nth month before Date.
e1 %m+% e2 add_with_rollback(e1, e2, roll_to_first = FALSE, preserve_hms = TRUE)
e1 |
A period or a date-time object of class POSIXlt, POSIXct or Date. |
e2 |
A period or a date-time object of class POSIXlt, POSIXct or Date. Note that one of e1 and e2 must be a period and the other a date-time object. |
roll_to_first |
rollback to the first day of the month instead of the
last day of the previous month (passed to |
preserve_hms |
retains the same hour, minute, and second information? If
FALSE, the new date will be at 00:00:00 (passed to |
%m+% and %m-% handle periods with components less than a month by first
adding/subtracting months and then performing usual arithmetics with smaller
units.
%m+% and %m-% should be used with caution as they are not one-to-one
operations and results for either will be sensitive to the order of
operations.
A date-time object of class POSIXlt, POSIXct or Date
jan <- ymd_hms("2010-01-31 03:04:05")
jan + months(1:3) # Feb 31 and April 31 returned as NA
# NA "2010-03-31 03:04:05 UTC" NA
jan %m+% months(1:3) # No rollover
leap <- ymd("2012-02-29")
"2012-02-29 UTC"
leap %m+% years(1)
leap %m+% years(-1)
leap %m-% years(1)
x <- ymd_hms("2019-01-29 01:02:03")
add_with_rollback(x, months(1))
add_with_rollback(x, months(1), preserve_hms = FALSE)
add_with_rollback(x, months(1), roll_to_first = TRUE)
add_with_rollback(x, months(1), roll_to_first = TRUE, preserve_hms = FALSE)Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.