R/ops-subtraction.r

In hadley/lubridate: Make Dealing with Dates a Little Easier

#' @include timespans.r
#' @include durations.r
#' @include intervals.r
#' @include periods.r
#' @include Dates.r
#' @include difftimes.r
#' @include POSIXt.r
NULL


subtract_interval_from_date <- function(int, date) {
  end <- int@start + int@.Data
  dur <- as.duration(int)
  add_duration_to_date(-dur, date)
}

#' @export
setMethod(
  "-", signature(e1 = "Duration", e2 = "missing"),
  function(e1, e2) multiply_duration_by_number(e1, -1)
)

#' @export
setMethod(
  "-", signature(e1 = "Interval", e2 = "missing"),
  function(e1, e2) multiply_interval_by_number(e1, -1)
)

#' @export
setMethod(
  "-", signature(e1 = "Period", e2 = "missing"),
  function(e1, e2) multiply_period_by_number(e1, -1)
)

base <- c("Date", "POSIXct", "POSIXlt", "numeric")
classes <- c("Duration", "Period", "Interval", base)
for (class_i in classes) {
  for (class_j in classes) {
    if (class_i %in% base && class_j %in% base) {
      break
    }
    setMethod("-", signature(class_i, class_j), function(e1, e2) e1 + (-e2))
  }
}