如果我明白你的意思，我们可以用模运算。
我会将一周中的每一天编码为一个从0开始的命名向量，然后使用一个小助手函数来计算差值mod 7。

days = c(
  Monday = 0,
  Tuesday = 1,
  Wednesday = 2,
  Thursday = 3,
  Friday = 4,
  Saturday = 5,
  Sunday = 6
)

day_diff = function(from, to) {
  unname((days[to] - days[from]) %% 7)
}

day_diff("Friday", "Tuesday")
# [1] 4 

day_diff("Saturday", "Sunday")
# [1] 1

day_diff("Sunday", "Saturday")
# [1]  6

您可以执行以下操作：

DaysOfWeek <- c("Monday","Tuesday","Wednesday","Thursday","Friday","Saturday","Sunday")

delivery_start <- 'Sunday'
delivery_end <- 'Tuesday'

delivery_days <- ifelse(which(DaysOfWeek == delivery_start) > which(DaysOfWeek == delivery_end),
                        7 + which(DaysOfWeek == delivery_end) - which(DaysOfWeek == delivery_start),
                        which(DaysOfWeek == delivery_end) - which(DaysOfWeek == delivery_start))

这个例子将返回结果2。

这里有一种可能性，你可以将一周中的天数向量加倍，然后找到两天之间的最短正距离：

DayofWeek <- rep(c("Monday","Tuesday","Wednesday","Thursday","Friday","Saturday","Sunday"), 2)

days_between <- function(day1, day2) {
  start <- which(DayofWeek == day1)
  end <- which(DayofWeek == day2)
  
  min(Filter(\(x) x > 0, sapply(end, `-`, start)))
}

输出

days_between("Monday", "Saturday")
[1] 5
days_between("Sunday", "Monday")
[1] 1