Subtract numerics from mondates.
When units = "months" and the numeric is a whole number
the result has the same
day of the month subject to the number of days in the month,
thus abandoning mondate's
approach of representing days as fractional months.
See examples.
subtract(e1, e2, units, forcelastday = FALSE)A mondate.
a mondate
anumeric
Anything allowed by base:::as.difftime.
In addition, can be "months" or "years".
If missing, defaults to timeunits(e1).
If FALSE, the result will have the same day of the month subject to
the numbere of days in the month.
If TRUE, the day of the month of the result will be the last day of the
month if e1 is on the last day of the month.
Dan Murphy.
x <- mondate(0:12)
subtract(x, 1) # The third date will the the 29th of March
x <- mondate.ymd(2013, 2:12, 15)
subtract(x, 1) # Always the 15th of the month. Compare to ...
x - 1
stopifnot(subtract(x, 1, units = "months") == mondate.ymd(2013, 1:11, 15))
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