subtract: Subtract numerics from mondates using day-of-month logic
In mondate: Keep Track of Dates in Terms of Months

Description Usage Arguments Value Author(s) Examples

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.

1	subtract(e1, e2, units, forcelastday = FALSE)

`e1`	a `mondate`
`e2`	a`numeric`
`units`	Anything allowed by `base:::as.difftime`. In addition, can be "months" or "years". If missing, defaults to `timeunits(e1)`.
`forcelastday`	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.

A mondate.

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))